Plant Kingdom
There are three major classifications that have been put forward for different plants and animals.
There have been early attempts for classification as done by the folowing:
A. Early Classification:
a) Aristotle: Grouped plants into trees , shrubs and herbs based on their habit. He divided animals into Enaima and Anaima on the basis of presence and absence of RBC respectively.
b) Charaka who was considered as the father of Ayurveda listed 200 kinds of animals and 340 kinds of plants in his book 'Charak Samhita.
B. Artificial system of Classification
It is a system of classification which is based on the morphological characters. The earlier system of classification was given by Aristotle who classified on the basis of habit and habitat. Besides him, It was Theophrastus, Pliny, Bauhin, John Ray, Linnaeus who proposed the artificial system of classification of plants. This classification was based on the number and situation of stamens, styles, and stigmas rather than evolutionary relationships.
- According to Theophrastus the plants were classified on the basis of their habit and thereby placed them into herbs, shrubs and trees.
-Carlous Linnaeus: ( 1707-1778) was considered as the Father of Modern Taxonomy. He classified the plants exclusively on the basis of the nature and number of stamens and carpels.He called it as the Sexual system of classification or numeric system of classification. He classified plants into 24 classes, in which 23 were of flowering plants ( Phanerogamia) and 24 th class had flowerless plant ( Cryptogamia). He proposed classes monandria (1 stamen) , Diandria (2 stamens) , tri and polyandria (3 or more stamens).
The details of his classification was published in Genera Plantarum (1737). The 24 classes named by him were: Monandria, Diandria, Triandria, tetrandria, Pentandria, Hexandria, Heptandria, Octandria, Ennendria, Decandria, Dodecandria, Icosandria, Polyandria, Didynamia, Tetradynamia, Monadelphia, Diadelphia, Polyadelphia, Syngenesia, Gynandria, Monoecia, Dioecia, Polygamia, Cryptogamia.
The artificial system of classification had a number of drawbacks, namely;
a) Since the system was based on limited characters , hence, the diverse groups of plants and animals were placed into limited number of groups.
b) There were no natural relationship amongst the organisms.
c)Leads to heterogenous assemblage of unrelated organisms.
d) No natural or phylogenetic relationships were considered.
C. Natural System of Classification
This system is based on natural afinities of plants. It is also known as the horizontal sytem of classification or 2'D' system. Various taxonomic characters are used to group the organisms. It is based mainly on the morphological relationships realizing all the information at the time of collection of plants. Some of the natural systems are:
a) A.L. Jussieu (1686-1758) attempted to clasify the plants in his book Genera Planatarum. He considered the number of stamnes with respect to the ovary and number of cotyledons. He considered 15 classes of plants.. these classes were further divided into 100 orders which were equivalent to the present day families.
b) A.p..de Candollow in 1819, classified the plants in his book ' Theorie Elementaire de la Botanique' . Characteristics of Vascular tissue was used for the system of classification. On that basis two major groups were recognized namely; vasculares ( vascular plans with cotyledons) including the groups Pteridophyta, Gymnosperms, Angiosperms and Cellulares ( Plants without vacular bundles and cotyledons) including the groups Thalophyta and Bryophyta.
c) George Bentham (1800-1884) and Joseph Dalton Hooker (1817-1911) proposed their system of classification in Genera Planetarium (1883) . In this system the Gymnosperms have been given an equal rank as that of Dicotyledons and Monocotyledons. This system has been followed by most of the herbaria of the world.
Merits of Natural system of classification :
It establishes natural relationship amongst organisms
It places only related organisms in a group.
It brings out the phylogenetic relationships and indicates the possible origin of different taxa.
An outline classification of phanerogamia is given as below:
Class Dicotyledonae:
General characters:
Pentamerous flower, reticulate venation in leaves, two cotyledons in seed, vascular bundles open with cambium , secodary growth present , wood formation occurs.
It is divided into 3 subclasses:
Subclass 1: Polypetalae- petals free and separate
It has three series:
Series1: Thalamiflorae: Flower hypogynous , Stamens and Pistils many ( indefinite) , petals free. Distinct sepals are free from ovary. It has 6 orders.
Series 2: Disciflorae: Flower hypogynous , Calyx consists of free or united sepals . Petals free. A prominent cushion shaped disc is present below ovary. It has 4 orders.
Series 3: Calyciflorae: Flower perigynous or epigynous , calyx contains united sepals ( rarely free) . Ovary inferior. It ha 5 orders.
Sub class 2: Gamopetalae- Petals united or fused.
It has three series:
Series 1: Inferae – Flower epigynous, ovary inferior, stamens as many as corolla lobes or fewer. It has three orders.
Series 2: Heteromerae- Ovary usually superior , carpels mor than two. It has 3 orders.
Series 3: Bicarpellate: Ovary usually superior, two carpels ( rarely one or three). It has 4 orders.
Sub class 3: Monochlamydaeae- Flower incomplete , no distinction between calyx and corolla . The presence of perianth is there which is usually sepaloid and may be absent.
It is divided into 8 series:
Series 1: Curvembryeae- Embryo carved , generally one ovule in ovary and one in each locule.
Series 2: Multivulatae Aquaticae: Plants are aquatic , submerged herbs, syncarpous ovary.
Series 3: Multivulatae Terrestres: Plants are terrestrial, syncarpous ovary.
Series 4: Microembryae; Very minute or small embryo.
Series 5: Daphnales- Ovary with one carpel and one ovule.
Series 6: Achlamydosporeae: Ovary unilocular with one to three ovules. Ovary inferior.
Series7: Unisexual: Flower unisexual
Series 8: Ordines Anomali- Families having plants with anomalous ( abnormal) characters.
Class 2: Gymnospermae
Sex organs on cones , perianth absent , ovule naked ( found inside ovary ) , seeds are also naked haploid endosperm.
It has families -Gnetaceae, Coniferae, Cycadaceae.
Class 3: Monocotyledonae
Parallel venation in leaves , embryo with one cotyledon , flower usually trimerous, wood absent, no secondary growth.
It has seven series:
Series 1: Microspermae: Ovary inferior, seed minute
Series 2: Epigynae: Ovary inferior, seeds larger
Series 3: Coronarieae: Ovary superior, perianth coloured
Series 4: Calycineae: Ovary superior, perianth green
Series 5: Nudiflorae: Perianth absent, ovary superior
Series 6: Apocarpae: carpels free ( apocarpous)
Series7: Glumaceae: Flowers arranged in spikelets with bracts.Perianth reduced , bracts large and scaly.
In this classification class is like division , series is like class, cohort is like order and order is like family.
Merits of Bentham and Hooker System of Classification:
(i) It is practically useful. It is considered to be the most useful system in India.
(ii) In this system of classification Monocots have been considered to be more advanced as compared to Ranales which have been considred to be primitive.
Demerits of Bentham and Hooker System of Classification:
(i) Gymnosperms were plced between dicots and monocots
(ii) Many important floral characters have been neglected.
(iii) This does not take the phylogenetic system into consideration, it believes in fixity of species.
(iv) There is a distinct discrimination; Some closely related families have been put under different cohorts while unrelated families have been placed nearer.
(v) Advanced family like Orchidaceace have been considered as primitive.
Phylogenetic System:
The evolutionary history of a group of organisms is called phylogeny.The term was coined by Lamarck. According to this system plants were classified in order of their evolutionary and genetic affinities. In this the organisms belonging to the same taxa have been believed to have a common ancestor and may be represented in the form of a family tree which is known as Cladogram.
A.K Eichler modified Bentham and Hooker's sysyem by placing gymnosperms in the beginning. He has been cosidered as the pioneer in the phylogenetic system of classification.
Adolf Engler and Karl A.E. Prantl. are two German botanists, who adopted the phylogenetic system of classification.
Merits of Phylogenetic system:
The families are arranged according to increasing complexity of flowers.
Demerits of Phylogenetic system:
(i) Monocots were considered primitive to dicots.
(ii) According to this form , primitive forms have naked flowers, which is placed in the beginning. The more advanced families have distinct perianth while the highly evloved families have fuse perianth.
John Hutchison presented the phylogenetic classification in his book” Families of Flowering plants” in 1959.
According to Hutchinson's classification:
(i)The trees and shrubs have been considered to be more primitive than the herbs.
(ii) The dicots have been considered more primitive than the monocots
(iii) Polypetalous actinomorphs and solitary flowers have been considered more primitive.
The outline classification of Hutchinson's Classification is as follows:
Divisions include order which in turn includes families. The division does not include classes.
'Taxonomy without Phylogeny is bone without flesh' – was stated by Takhajan
Branches of Taxonomy:
1.Classical Taxonomy:
(i)It deals with employing all available information to classify organisms on the basis of their origin , evolution, affinities and variations.
2. Numerical taxonomy/ Phenetics/ Taximetrics/ Adansonian taxonomy
(a) Uses statistical methods for evaluating similarities and differences between species. All selected characters have been given equal importance. The comparisons have been made easier by the use of calculaing machine and computers.
(b) Dendrogram is family tree of organisms on the basis of numerical taxonomy.
3. Biosystematics:
It deals with variations within a species and its general evolution.
4. Cytotaxonomy/ Karyotaxonomy:
based on the cytological information on cell, chromosome number, their structure and behaviour, during meiosis.
5. Chemotaxonomy:
based on the chemical constituents of plants i.e. Betacyanin pigment in beet roots, raphides and cystolith, sequencing of DNA and chemical nature of proteins.
Taxonomy was divided into three parts by Turril:
(i) α taxonomy: based on gross morphological features including compilation of monographs and flora
(ii) β taxonomy: based on morphology and evidences from genetics, cytology, anatomy, physiology etc.
(iii)Ω taxonomy: It includes all microscopic and biochemical evidences.
Classification of Plant Kingdom
The major groups of Plant kingdom include:
a) Thallophyta
b) Bryophyta
c) Pteridophyta
d)Gymnosprms
e) Angiosperms
1. THALLOPHYTA- ALGAE
The thallophytes are polyphyletic group of non-mobile organisms traditionally described as relatively simple plants or lower plants with undifferentiated bodies (thalli)
General characters of algae:
1) Eukaryotic, autotrophic, chlorophyllous, cryptogamic, thallophytes.
2) They are aquatic forms, either fresh water or marine forms.
3) Available in many forms: Unicellular ( Chlamydomonas), In colonial form ( Volvox), palmelloid ( Tetraspora), dendroid ( Prsinocladius), filamentous unbranched ( Spirogyra) or branched ( Chladophora), heterotrichous ( Fritschiella, Coelochaete, Stigeoclonium), siphonaceous (Vaucheria), parenchymatous (Ulva)
4. The food is stored in the form of starch.
5.Reproduction:For aquatic organisms such as algae, dispersal and desiccation stresses are at a minimum.
(a) Vegetative reproduction;It takes place by fragmentation.
(b)Asexual reproduction : It takes place by zoospores, aplanospores, hypnospores, akinetes, palmella stage, autospores.
(c)Sexual Reproduction: Sex organs are unicellular or multicellular, with all fertile cells and non-jacketed. The embryonic stage is absent. There are three types of gamets namely (i) isogamous (ii) Anisogamous (iii) Oogamous. Sporic or Gametic or Zygotic meiosis occurs in the life cycle.
Algae was classified into 11 classes by F.E. Fritsch in his book titled “ Structure and Reproduction of the Algae” mainly on the basis of pigmentation , reserve food, flagellation, thallus structure, mode of reproduction and life cycles.
Whitaker included only Chlorophyceae ( green algae), Phaeeophyceae ( brown algae) and Rhodophyceae ( red algae) in algae under Kingdom Plantae.
( a) Green algae ( Chlorophyceae):
General Characteristics:
(i) Exist in mostly fresh water forms ( Spirogyra, Ulothrix, Chara, Chlamydomonas, Volvox ) and marine forms as well ( Acetabularia, Ulva)
(ii) Photosynthetic pigments are chlorophyll a , chlorophyll b and carotenoids.
(iii) Isokont flagellation
(iv) Thyllakoids are in group of 2-20 per lamella.
(v)Pyrenoides present.
Three types of life cycle occurs in the Green Algae:
(a) Haplontic Life Cycle: e.g. Ulothrix, Spirogyra, Chlamydomonas ( Zygotic meiosis occurs)
(b) Diplontic Life cycle e.g. Caulerpa ( gametic meiosis)
(c) Diplohaplontic life cycle e.g. Ulva, Cladophora. The haploid and diploid phases are well developed and multicellular. The isomorphic alternation of generation is found.
1.Chlamydomonas:
Chlamydomonas is microscopic, unicellular green plants (algae) which lives in fresh water. Typically their single-cell body is approximately spherical, about 0.02 mm across, with a cell wall surrounding the cytoplasm and a central nucleus.Two filaments of cytoplasm, flagella, extend from one end, and their whip-like lashings pull the chlamydomonas through the water and rotate it at the same time. A single, cup-shaped chloroplast occupies the greater part of the cell. In this chloroplast is a protein region called a pyrenoid, which is involved in starch production and is often surrounded by starch granules. The cell wall is made up of hydroxyproline (glycoprotein).Presence of neuromotor apparatus ) basal granules + paradesmos + rhizoplast + centrosome ). Two contractile vacuoles, single eye spot or stigma as photoreceptor organ are present.
Red snow is caused by hypnospores of Chlamydomonas nivalis. Haematochrome , a carotenoid pigment is present in them.
Bald spot: receptive, colourless spot of oogonium through which male gamete enters.
Reproduction:
Asexual reproduction by zoospore, aplanospore, hypnospores, and palmella stage.
Asexual reproduction:
(i)By zoospore : Under favourable conditions
(ii)By Palmella stage: Formed in response to dessication conditions and toxic salts. The spores sre green , non-motile and are capable of growth and division.
(iii) By aplanospore ( thin walled spore ) or hypnospores ( thick walled spores). These are formed under drought conditions. e.g. Chlamydomonas caudata.
Sexual reproduction:
It is of the following types:
(i) isogamy ( fusion of similar gametes) e.g. Chlamydomonas debaryana ( homothallic) or Chlamydomonas reinhardii ( heterothallic).
(ii) Anisogamy ( fusion between a motile, smaller, male gamete and a motile larger morphologically dissimilar female gamete ) e.g. Chlamydomonas braunii.
(iii) Hologamy ( fusion of young cells ) e.g. Chlamydomonas media
(iv) Oogamy: ( fusion between a motile male amete and a non-motile female gamete ) e.g. Chlamydomonas coccifera.
2. Spirogyra
It is commonly called as summer alga or hair of princess or pond silk or water silk or pond scum ( due to mucilage covering found in stagnant water. .They are a free-floating filamentous form of green algae, commonly seen as bright green masses on the surfaces of freshwater ponds and ditches. It is a genus of green algae, belonging to the order Zygnematales. The name 'spirogyra' is derived from the spiral arrangement of chloroplast in its filament-like body. Spirogyra cells are cylindrical in shape and are connected end to end, forming a long, unbranched filament-like structure. The cell wall is made up of an outer layer of cellulose and an inner layer of pectin. The inner surface of the cell wall is lined with a thin layer of cytoplasm. The spiraled ribbon-shaped chloroplasts are embedded in the cytoplasm lining. The number of chloroplasts in each cell may vary from one to sixteen. Each chloroplast has several round bodies called 'pyrenoids', which are responsible for the production of starch. Each cell has a prominent nucleus in the center, suspended by thin strands of cytoplasm from the inner part of the cell wall. The cells are long and thin, and each spirogyra filament measures between 10 to 100 micrometer in width. Sometimes, these filaments have root-like structures, which help them attach themselves to the substratum.
Spirigyra adnata and Spirogyra jogensis are attached to the subsratum by basal cell called holdfast or hapteron.
Reproduction :
Spirogyra shows three kinds of reproduction namely: vegetative, asexual and sexual.
(i) Vegetative reproduction : By fragmentation.
(ii) Asexual reproduction :
a) By parthenogenesis or azygospores: e.g. Spirogyra varians, when placed in the sugar solution , develops parthenospores.
b) By akinetes: e.g. Spirogyra farlowi
c) By aplanospores
Sexual Reproduction:
It occurs by conjugation. Physiological anisogamous type.
Types of conjugation:
a) Scalarifirm conjugation: It is the most common type of conjugation. Occurs in heterothallic and homothallic species. Minimum two filaments are involved e.g. Spirogyra tuwensis.
b) Lateral conjugation: Two adjacent cells of same filament function as gametangia. e.g. Spirogyra affinis.
Economic importance of green algae:
(i) Codium and Ulva ( Sea lettuce) is used as salad or vegetable in Europen countries after drying and salting.
(ii) Chlorella pyrenoidosa ( space alga) is used by exobiologists for food , oxygen and disposal of CO2 and organic waste in prolonged space flight.
(iii) Cephaleuros virescence : It is parasitic green alga which causes red rust of tea disease.
Brown Algae ( Phaeophyceae):
General Characters:
(i) The members of this group are called brown algae due to their characteristic brown colour obtained from the pigment present fucoxanthin.
(ii) The brown algae are marine in nature exclusively found primarily in the coastal region. They are found in the cooler seas. Sargassum is a warm water form that occurs in the North Atlantic Ocean region and forms Sargasso sea.
(iii) The brown algae is never unicellular. Most of the brown algae are macroscopic except a few which are microscopic. The massive size algae are Laminaria (2-9 mts) Nereocystis (45 mts) ; Macrocystis (60-90 mts) . Because of their bulky appearance , thay are called giant kelps.
(iv) The body of a typical brown alga ( Laminaria) is differentiated into holdfast, stipe and lamina.In some large brown algae, certain cells are modified to form long filaments called trumpet hyphae. These carry food from lamina to the holdfast.
(v) The cell walls of brown algae are generally composed of twolayers -an inner cellulosic layer and an outer mucilaginous layer.The cellulosic walls are coveres by a colloidal covering called phycocolloids.
(vi) Alginic acid is an important component of the phycocollois and is comercially obtained from kelps. It has haemostatic properties and has been used in emergency transfusions in the treatment of shock. Sodium alginate has been used as a stabilizer in food industries; calcium alginate in plastics. Forms of alginic acid are used in textile, rubber and paint industries. It is used for making the ice creams smooth.
(vii) The cell of brown algae contain fucosan vescicles. The functions of which are not known.
(viii) The cells contain a pigment fucoxanthin in addition to chlorophyll a and c. Fucoxanthin dominates over the green colour of the chlorophyll , imparting brown colour to the algae.
(ix)The reserve food material in the algae is in the form of laminarin starch and mannitol.
(x) Asexual reproduction occurs by motile or non-motile spores formed inside large sized cells called sporangia which may be unicellular or multicellular.
(xi) Sexual reproduction takes place by the formation of flagellate gametes which are formed inside the gametangia.In some cases the female gamete is non- motile. The gametes may be isogametes, both similar) , or anisogametes ( both similar but female larger in size), or oogametes.
( female large non- motile, male motile , small)
Economic Importance of Brown algae:
(i) Fucus and Laminaria are rich source of Iodine.
(ii) Laminaria yields a food product which is rich in carbohydrate called Kombu and Alaria produces Sarumen in Japan.
(iii)Durvillea has antiworm properties.
Red algae( Rhodophyceae):
General Characters:
(i)The red colour of the red algae is because of the presence of r-phycocyanin and r-phycoerythrin.Mostly marine.
(ii)The thallus of red algae varies from being microscopic, unicellular to half a meter in length. These may be unicellular, filamentous, ribbon shaped or leaf like. Some of these secrete calcium carbonate over their walls and form coralline structures. Corallina , a red alga is the main producer in some coral reefs.
(iii) In deep oceans they acquire deeper color. Only the blue green light reaches the deep water. The pigments r-phycoerythrin in red alga captures light of available wavelength for the red lagae.
(iv) Some red algae are also parasitic in nature. e.g. Herveyella is parasitic on other red algae. The parasitic forms , however , are colourless.
(v) The cell wal contains cellulose and pectic material along with some polysaccharides called photocolloids , some of which might contain sulphur e.g. Agar. Agar is widely used to prepare solid food nedia for the growth of bacteria and fungi in the laboratory, although it has no food value for the bacteria and fungi. Human beings also use agar as a thickening and binding agent in various food products.Agar-agar is obtained commercially from algae Gelidium and Gracilaria.
(vi) Carageenin is a biochemical substance present in the cell walls of red algae which is used as thickening and binding agent in food products like pudding etc.
(vii) The cells appear in uninucleate or multinucleate forms with one or more plastids. That may be with or without pyerenoids. The food reserve lies in the form of Floridan starch and a soluble sugar fluoridodoside.
(viii) Asexual reproduction takes place with the help of non motile spores. Fragmentation is the common mode of reproduction, Although some of the red alga is able to regenerate the full plant from the severed holdfast.
(ix) The red alga exhibits highly advanced form of sexual reproduction. It is also oogamous. Flagellated gametes are absent in red algae. The male gametes are known as spermatia which are developed in the special type of structures called spermatangia while the female cells are known as carpogonia. The carpogonium is a flask shaped structure having a neck like trichogyne.
(x) Alternation of generation in haploid and diploid stages are seen to occur in many algae.
2.Bryophyta
General Characteristics:
1. They are found in moist and shady places i.e. Sciophytes. They usually grow during damp season , forming green carpets, on rocks, walls, tree trunks etc.
2. There are exceptions that is they also exist in aquatic forms: (i) Riccia fluitans, (ii) Ricciocarpus ntans (iii) Riella; Fontinalis saprophytic forms.: (i)Cryptothallus mirabiliis, (ii) Buxbaumia aphylla, and epiphytic form (i) Frullania.
3.The dominant phase or plant body is a free living gametophyte.
4.No vascular tissue in either generation. Root-like structures are rhizoids.
5.The rhizoids may be unicellular or multicellular.
6. The vegetative reproduction is common by fragmentation, tubers, gemmae, buds, adventitious, branches etc. Mitospores are not formed.
7. Sexorgans are multicellular and jacketed. They are of two types, male antheredium and female archegonium.
8. An external layer of water is essential for the swimming of male gametes and to reach the archegonia.
9. Fertilization produces an embryo iside the archegonium. The embryo grows into a sporophyte
10. The sporophyte is parasitic over the gametophyte.
11. The sporophyte of bryophytes is known as sporogonium. It produces haploid spores inside its capsule part while still being attached to the gametophyte.
12. On germination each spore produces a gametophyte either directly or through a juvenile filamentous stage called protonema.
13. The alternation of generation is either heteromorphic or heterologous.
Classification of Bryophyta
Bryophyta
Classes Hepaticopsida Anthoceropsida Bryopsida
(Liverworts) (Hornworts) (Mosses)
e.g. Riccia, Marchantia e.g. Anthoceros e.g. Funaria (cord moss)
Life cycle of Funaria Hygrometrica
Funaria is a radially symmetrical plant differentiated into stem, or central axis, leaves, or phylloides and rhizoides. The rhizoides are multicellular , branched, with oblique septa. It is monoecious and autoicous ( both sex organs are on the same plant but on different branches). The Antheredia are borne at the tips of the main axis and surrounded by perigonial leaves. Archegonial clusters are borne on lateral branch tip and are surrounded by perichaetial leaves. Both male and female gametangia are acrocarpous. Male gametes or sperms are elongated , biflagellate and has a curved body. The archegonium has 6-10 neck canal cells.
Diploid oospore develops into sporophyte. Mature sporogonium is differentiated into foot, seta and capsule. Foot is embedded in gametophytic plant body, meant for absorption of water , mineral salts and fixation. Seta is a narrow stalk which lifts the capsule in the air. Capsule is differentiated into three parts -apophysis, theca and operculum.
Apophysis contains assimilatory tissue, stomata with singular annular guard cell. Theca contains central sterile columella , a spore sac, air cavity and assimilatory tissue. Operculum is separated from theca by one celled elongated diaphragm. The annulus lies above the rim.
Peristomial teeth are 32, acellular, arranged in 2 rings of 16 each. The outer periosteum teeth are exostome, bear transverse thickening of cellulose, showing hygroscopic movement. Endostome or inner peristomel teeth are without cellulose thickening, acts as sieve and checks sudden dispersal of spore .
Some common names:
Some facts:
(i)Smallest bryophyte is Zoopsis
(ii) Largest bryophyte is Dawsonia
(iii) Largest archegonium in plant kingdom is of Funaria.
(iv)The term Bryophyta was coined by Robert Brawn (1864) but it was delimited in its form by Schimper(1879).
3. Pteridophyta
General characters:
(i)The term pteridophyta was coined by E.Haeckel for plants with feather like fronds.
(ii)They are the first group of tracheophytes. The plant body is sporophytic.Sporophyte plant body has true roots, stem and leaves with well developed vascular system.
(iii)Meiospores are formed inside sporangia. These sporangia are associated with leaves called sporophyll.
(iv)Most pteridophytes are homosporous; only a few show heterospory.Spores are produced in multicellular sporangia after meiosis in spore mother cells.
(v)The life-cycle shows distinct heteromorphic alternation of generations.
(vi)Diploid sporophyte generation is predominant.
(vii)Asexual reproduction takes place by spores.
(viii)Gametophyte is haploid, multicellular, green and an independent structure.
(ix)Sex organs, antheridia and archegonia are multicellular.
(x)Antherozoids (sperms) are spirally coiled and multi flagellate.
(xi)Opening of sex organs and transfer of male gametes to archegonium for fertilization are dependent on water. Further, fertilization takes place inside the archegonium.
(xii)Vascular tissues are present. They are of two types, xylem and phloem. In xylem true vessels are absent. In phloem , companion clls are absent and sieve cells are present.
(xiii)Sporangium development is of two types:
(a) Leptosporangiate: When sporangium develops from single superficial cell. e.g. Pteris, Dryopteris, Adiantum.
(b) Eusporangiate: Sporangium develops from single superficial cells.e.g. Selaginella , Equisetum.
(xiv) Sex organs are multicellular and jacketed . Antheredia are reduced.Archegonia are partially embedded.
(xv)The embryo stage is present and the embryogeny is of two types:
Development of embryo :
(a)Holoblastic- When the entire zygote is involved in embryonic development.e.g. Ferns.
(b)Meroblastic – when the part of zygote is involved in embryonic development e.g. Selaginella
Some common examples of microphyllous pteridophytes (i.e., poorly developed leaves) are club mosses (Lycopodium sp.), and whisk ferns (Psilotum sp.). Examples of megaphyllous (large-leafed) pteridophytes are the ferns Nephrolepis, Osmunda, Pteris, and Salvinia.
The steeler theory was proposed by VanTeigham and Douliot.
Types of Steles
TYPES OF STELES
A. Simple protostele
A'. Actinostele
A''. Plectostele
B. Ectophloic siphonostele
B'. Amphiphloic siphonostele (solenostele)
B''. Dictyostele
C. Eustele
D. Atactostele, the only stele type not found in the ferns
Siphonostele : It has evolved from the protostele. In siphonostele, pith is present in the center of the xylem cylinder. The phloem is external to xylem.
Solenostele : A Cbroken at one point at a time due to the non-overlapping leaf gaps is called solenostele
Dictyostele : Siphonostele in which many overlapping leaf gaps occur at the same level is called a dictyostele, or dissected siphonostele. In a transverse section it appears broken into many smaller or larger arcs. Each arc is known as a merestele (e.g. fern rhizome). Each meristele is completely and independently surrounded by the pericycle and the endodermis. This is the most highly- evolved stele type in Pteridophyta.
Eustele : The characteristic stele present in dicot and gymnosperm stems is called a eustele (i.e." true" stele). It is also a dissected siphonostele in which the vascular cylinder is dissected into separate vascular bundles arranged in a ring. The entire ring of vascular bundles is surrounded by the pericycle and the endodermis.
Atactostele : This is a complex type of stele in which numerous vascular bundles remain irregularly scattered in the ground tissue (atactos means without any order). Atactostele is a characteristic of monocot stems. Here, due to the scattered vascular bundles, the cortex and stele are not demarcated. Similarly, the endodermis and the pericycle are not differentiated.
Life Cycle of Selaginella:
The plant body is an evergreen sporophyte. It is differentiated into stem , leaves and roots. The roots develop at the tips of rhizophores.
Salient features:
1. Plant body is an evergreen sporophyte. It is differentiated into stem , leaves and roots. The roots often develop at the tips of special structures called rhizopores.
2. Vegetative growth is by fragmentation , bulbils and tubers. The function of bulbils and tubers help in perennation.
3.Sporangia develop in the axil of fertile leaves or sporophylls at the tips of small branches called spikes. There are two types of sporangia, micro and megasporangia.
4. Each microsporangium produces a large number of small haploid microspores . A mgasporangium develops only four haploid megaspores. Growth of the gametophyts is precocious.
5..The plants exhibit dorsiventral or radial symmetry. All the vegetative parts contain vascular tissues, which are organized in steele.
6.The xylem mainly consists of traceids and xylem parenchyma . The vessels are generally absent but the primitive types are found in Selaginella, Equsetum, Pteridium.
7.The phloem consists of sieve- tube and phloem parenchyma. The companion cells are absent.
8. Microspore produces an endosporic 13 celled male gametophyte. This gametophyte has one prothallial cell and jacket cells and 4 androgonial cells. The androgonial cells give rise to 128-256 androcytes or sperm mother cells. A sperm cell gives rise to a biflagellate sperm.
9. The megaspore produces exosporic female gametophyte. The female gametophyte contains an exposed generative apical cuushion and storage tissue as well. A diaphragm separates the two. The apical cushion produces archegonia and rhizoids. Each archegonia has a single female gamete or oosphere. Fertilization requires external water for the swimming of sperm. Diploid oospore is produced.
10.Oospore divides to produce a suspensor and embryo. The development of embryo is meroblastic. Suspensor pushes the embryo into the food laden storage tissue. The embryo has a foot for absorbing the nourishment, moreover, it also has a shoot tip and a root tip. These two elongate to produce an independent sporophytic plant body.
11. Selaginella shows two distinct generations , i.e. The sporophytic and the gametophytic, one producing the other. Morphologically they differ from each other. The phenomenon is termed as hteromorphic or heterologous alternation of generation.
12. Under dry conditions , the xerophytic species of Selaginella roll into brown balls. The phenomenon is known as cespitose habit. They may remain uprooted under this condition. But during moist conditions these brown balls become green and unroll again under moist conditions. Therefore, these plants are calles aas resurrection plants. e.g. Selaginella lepidophylla,
Selaginella bryopteris.
13. Plant body of Selaginella chrysocaulos and Selaginella selaginoides is erect. The leaves are isophyllous and arranged in two rows. The plant body of Selaginella is prostrate. The leaves of this are anisophyllous or dimorphic and arranged in four rows.
14. The stem in Selaginella is distelic. Rarely stem is monostelic.
15. Bower and Goebel named rhizophore of Selaginella as an organ sui-generis, i.e. Bearing the characteristics of both stem and root but independent in origin.
16. The mucilage oozing out of the neck of the archegonium in Selaginella and Fern contains malic acid. The neck of archegonium in Selaginella and fern contains only one neck canal cell.
17. Selaginella rupestris shows seed habit.
Ferns (Pteridophytes)
1) The plant body is a sporophyte. It is differentiated into true stem, leaves and roots.
2) Most of the ferns have underground rhizome. Some are called tree ferns.e.g. Cyathea, Celotia.
3) The venation is furcate type in which the veins branch dichotomously without forming interconnections.
4) The younger parts of stem, young leaves, petiole and rachis of mature leaves possess hairs or scales called ramenta. These protect them from mechanical injury and dessication.
5) Young leaves show circinate ptyxis , that is they have a coiled appearance. This coiling protects the growing tip which comes to lie in the centre.
6) Sporangia occurs on the leaves in clusters called sori . The fertile leaves are known as sporophylls. A sorus is covered by a flap like outgrowth from its surface ( true indusium, e.g. Dryopteris) or turned margin of the sporophyll ( false indusium, e.g. Adiantum)]
Life cycle of Dryopteris:
The salient ffeatures are as follows:
a) It is found in moist shady places. Located in tropical and subtroical areas.The plant body is perennial. They are independent, living , evergreen . The sporophyte has vascular tissues. The body is differentiated into stem , roots and leaves. The roots are adventitious. Stem is an underground dark brown rhizome.The large aerial leaves or fronds are incompletely bipinnate compound leaf. The young leaves show circinate ptyxis. Persistent leaf bases of the dead leaves are found in older parts of rhizome.
In Dryopteris a leaflet has a single midrib giving rise to lateral veins showing dichotomous divisions. The young leaves , young parts of rhizome , petiole, and rachis of mature leaves are covered over by brown to black scales called paleae or ramenta.
(b) Reproduction:
The fern reproduces vegetatively by fragmentation of rhizome and develops adventitious buds. In Dryopteris the adventitious bud present at the leaf base separates and grows into a new plant. As the leaf bud touches the soil, a new plant develops. Cosequently the fern spreads over a large area. An example is Adiantum caudatum, which is also termed as the walking fern, and maiden hair fern.
The
leaflets of a mature leaf bear sporangia in clusters called sori. The
leaflets containing the sori is called sporophyll. In Adiantum the sori
are borne submarginally at the distal end on the under surface of the
leaflets. The margin of the leaflets cover the sorus. The reflexed
margin of the sorus is known as false indusium. . In Dryopteris the sori
develop in two rows, one on either side of the midrib. Each row
contains 4-6 sori , similar sori may contain 1-2 sor, or may be sterile.
Each sorus has a membranous sheath of it own, and this covering is
called true indusium. The covered sori of Dryopteris are kidney shaped
in outline. Therefore Dryopteris is also known as male shield fern.
A sorus consists of parenchymatous cushion or placenta. The placenta bears a number of stalked biconvex sporangia. In each sporangium there is a single layered jacket that encloses 12-16 diploid spore mother cells. A marginal row of jacket cells are differntially thickened to form annulus. The remainng marginal cells constitute stomium. The diploid spore mother cells divide meiotically to form haploid spores. As the spores mature the indusium shrivels. The exposed sporangia dehisce in the region of stomium due to differential contraction of annulus. The spores are dispersed by air currents.
As the spores fall on the suitable soil , each spore germinates and forms thalloid gametophyte called prothallus. It is a cordate, green and the structure is flat. Prothallus bears antheridia and archegonia at the ventral surface
The antheridium has 3 celled jacket and 32 mother cells. The sperms are multiflagellate and spirally twisted. The archegonium is flask shaped and has a single binucleate neck canal cell, single ventral canal cell and an oosphere. Sperms are attracted to the opened archegonia by malic acid present in their mucilage. Diploid oospore gives rise to an embryo which grows in size to form the fern plant.
Gymnosperms
(i)Gymnosperms are seed plants that do not produce flowers. The term gymnosperm means "naked seed." However, usually when the seeds of gymnosperms are immature they are enclosed within and protected by modified leaves or a cone.
(ii)All gymnosperms are perennial woody plants forming either bushes or trees. Some are very large and live for about a thosand years. e.g. Sequola sempervirens.
(iii)Leaves are generally dimorphic , foliage and scaly types.
(iv)There are four groups of gymnosperms living today—Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta.
(v) All gymnosperms produce at least some secondary growth, . The most abundant product of secondary growth is the secondary xylem (xylem is the water-conducting tissue of plants), or wood
(vi)The foliage leaves do not have lateral veins. Transfusion tissue occurs internally for lateral transport.
(vii) The wood is homoxylous but Gnetales bear vessels in xylem. e.g. Ephedra, Gnetum, Welwitschia.
(viii) Types of wood:
(a) Manoxylic : Soft wood, vaculat tissues with medullary rays, commercially less important e.g. Cycas.
(b) Pycnoxylic: Compact wood without or with narrow medullary rays, comercially more important e.g Pinus.
(c) Monoxylic: With single persistant cambium rings and bundles. e.g. Cycas.
(d) Polyxylic: With many persistant cambium rings and bundles e.g.Cycas
(ix) Flowers are absent. There are two types of sporophylls, microsporophylls and megasporophylls.
(x) The two types of sporophylls are usually aggregated to form distinct cones or strobilli, pollen cones, ( male cones) and seed cones ( female cones).
(xi) Seeds do not occur inside a fruit. They are naked or lie exposed on the surface of megasporophylls.
(xii) Ovule lie exposed on the megasporophyll. Ovules are unitegmic and orthotropous.
(xiii) Pollination is direct as stigma is absent and the pollen grains directly reach the micropylar ends of ovules. Pollination is usually accomplished by wind ( anemophily).
(xiv) Male gametophyte produces only two male gametes or sperms. Generally only one is functional.
(xv) External water is not required as a medium for transport of male gametes. A polen tube is formed by the male gametophyte for affecting fertilization.
(xvi) Seeds contain a food laden tissue for future growth of embryo into seedling.
Pinus is a coniferous gymnosperm having pyramidal or excurrent shape like a christmas tree. Sporophytic plant body divided in stem, leaves and roots. Stem branches are of two types , long and dwarf. The dwarf branches have 1-5 needle - like foliage leaves which are surrounded by a sheath of scale leaves.
Number of needles are 1,2,3,4 and 5 in Pinus monophylla, Pinus sylvestris, Pinus roxburghi, P. quadrifolia, and Pinus wallichiana respectively. The root system is tap root, with long horizontal types. The mycorrhizal roots lack root hairs and root cap; and they occur near soil surface.
Vegetative reproduction is absent. Pinus is monoecious and develops into clusters of shortly stalked male cones subterminally on the lower branches and female cones in circle of 2-6 on upper long branches.
Male cone has a short stalk, a central axis and a number of spirally arranged microsporophylls. It bears two oblong , parallel microsporangia on its lower surface. In microsporangium the diploid microspore mother cells undergo meiosis and form haploid microspores or pollen grains.At maturity the pollen grains are released from the male cones and dispersed by air currents. Pollen grains have two prothallial cell, a generative cell and a tube cell. They form yellow clouds in the pine forests. A pollen grain has two air sacs or wings for making it light.
The female or seed cones develop in groups 2-6 on upper long branches of the tree. Each female cone has a long stalk and a central axis on which are borne a number of spirally arranged paired scales. The lower pair is called bract scale while the upper scale is ovuliferous scale or megasporophyll. The ovuliferous scale bears two ovules towards the basal region on the upper side. The ovule consists of a 3- layered integument witha wide micropyle and nucellus. A megaspore mother cell differentiates in the middle of nucellus.
4 haploid megaspores are formed by meiosis, but only one survives. The functional megaspore gives rise to female gametophyte. The female gametophyte bears 1-8 archegonia. An archegonium has a short neck and broad venter. Neck canal cell is absent. The venter canal is ephemeral. The oospore is contained in the venter.
The female cones open when they are ready to pollinate. The pollination is anemophilous i.e. By air. And direct. The pollen grains pass into the opened micropyle and rest on the top of the nucellus. The micropyle of each ovule contain a mucilage or pollination drop for catching the pollen. The germination takes place and pollen tube is formed but further growth is arrested due to oncomung winter season. In the spring of next year the fertilization takes place i.e 13 months after the pollination. The pollen tube grows and pierces the archegonium . The male gamete fuses with the female gamete to form a diploid zygote. This oospore in turn produces an embryo while the ovule matures into a seed. A part of the upper surface of the ovuliferous scale is peeled off along the seed to form a wing. A female cone takes 26 months to be mature . It then opens to release winged seeds which are dispersed into the air. On falling onto a soil each seed gives rise to a new plant.
Some facts about Pinus:
i) The number of cotyledons in Pinus range from 3-18
ii) The proembryo has 4 tiers i.e. The basal embryo tier, suspenser tier, rosette air, and upper tier.
Iii) Resin is collected by injuring Pinus. It is a semifliud secrested by special tubes. It solidifies on exposure to air, thereby plugging the places of injury. It acts as an antiseptic and commercially distilled to obtain turpentine and resin. The resin is used in water proofing, sealing joints and preparation of writing paper. Turpentine is used as solvent in paints , polishes and wax.
Angiosperms:
They are the flowering plants. These are the most advanced plants characterized by the presence of flower , covered ovules and seeds. They comprise the largest group in the plant kingdom. Present in all kinds of habitat and have gone through evolution since the cretaceous period. Angiosperms include hydrophytes, xerophytes, epiphytes, parasitic, saprophytic , insectivorous, symbiotic and mangrove kinds.
Characteristic features of Angiosperms:
(i) Flowers are present along with the sex organs.
(ii) Ovules covered and placed within the ovary.
(iii) The carpel receives pollen grains in its stigma.
(iv) Syngamy is typical of angiosperms
(v) A triploid endosperm is formed after fertilization.
(vi) Xylem and Phloem contain vessels and companion cells respectively.
(vii) The fertilized ovum ripen into seeds and the seeds are covered by fruits. The fruit is technically considered to be a ripened ovary. These fruits protect the seeds and help in their dispersal.
(viii) Xylem contains vessels and Phloem contains sieve tubes as well as companion cells.
(ix) A gametophyte can be haploid or diploid but always produces gametes.
(x)The monocots grow in length and not in width. They produce new leaves and flowers.
(xi) Dicots have an indefinite growth and new roots, shoots leaves, bark, and wood are formed every year.
(xi)Petals are attractive and showy and attracts insects and other pollinators.
(xii) The pollination occurs by animal insects, worms, birds, bats and at times humans also.The insects accomplished pollination is termed as entomophily.
(xiii) The angiosperms are divided into two subgroups:
a)Dicots :They are the flowering plants characterized by the presence of two cotyledons in the seed, with reticulate venation in leaves, concentric tissue in the stem with open vascular bundles arranged in a ring, penta or tetramerous flowers.
b) Monocots: They are flowering plants which are characterized by the presence of a single cotyledon in the seed. The venation is of the paralel kind ie the leaves , with scattered closed type of vascular bundles in the stem and flowers are trimerous e.g. Banana, cereals, palm, grasses, bamboo, orchids etc.
Difference between various plant groups
Llife Cycle and Alternation of Generation
The haploid-diploid life cycle is the most complex life cycle and thus has lots of variation. It is also the most common life cycle among plants since all land plants, the vascular plants and the bryophytes, are haploid-diploid. An alternation of generations defines the haploid-diploid, or 1n-2n, life cycle. This occurs when a multicellular 2n sporophyte (SPT) phase alternates with a multicellular 1n gametophyte(GPT) phase.
In plants, the alternation involves alternating generations of haploid and diploid organisms. Often one of these generations is the dominant form of the organism, and the other generation is nutritionally dependent upon it or just grows as a smaller plant. For example, in mosses and liverworts, the haploid phase is the large, familiar form of the plant. The diploid phase is smaller and grows upon the haploid phase. In angiosperms, however, the diploid phase of the organism is large and independent, while the haploid phase is reduced to the pollen grain and the eight-celled female gametophyte located in the ovule.
Types of Life cycle or patterns of Alternation of Generation:
There are three main types of life cycle. These three types of cycles feature alternating haploid (n) and diploid (2n) phases.The haploid organism becomes diploid through fertilization, with joining of gametes. This results in a diploid zygote. To return to a haploid stage, meiosis must occur.
The cycles differ in the product of meiosis, and whether mitosis (growth) occurs. Zygotic and gametic meiosis have one mitotic stage and form during the n phase in zygotic meiosis and during the 2n phase in gametic meiosis. Therefore, zygotic and gametic meiosis are collectively term haplobiontic (single meiosis per phase). Sporic meiosis, on the other hand, has two meiosis events (diplobiontic): one in each phase.
They are as folows:
a) Haplontic Life cycle:It is characterized by the dominance of haplophase. The plant body is a gametophyte and independent. The sporophyte is dependent on gametophyte and is not free living The major part of life is gametophytic. e.g. Chlamydomonas, Ulothrix, Spirogyra
b)Diplontic: The diplophase is dominant here. The main plant body is a sporophyte , being independent and free living. The gametophytes are extremely reduced and are dependent physically as well as nutritionally on te sporophyte. The major part of the life cycle is a sporophyte. e.g all gymnosperms and angiosperms; diatoms, some brown algae i.e Fucus and Sargassum.
c)Diplo- haplontic life cycle: Characterized by the existence of sporophyte as well as gametophyte. Both of them are photosynthetic and free living. The phases diplophase and haplophase are equal. If the sporophyte and gametophyte are morphologically different then the life cycle is Diplo-haplontic -heteromorphic type. e.g. All Pteridophytes; all bryophytes, some algae and Kelps. When the life cycle is morphologically identical then the life cycle is termed as Diplo-haplontic -isomorphic e.g. Green algae i.e Ulva, Cladophora etc.
There are three major classifications that have been put forward for different plants and animals.
There have been early attempts for classification as done by the folowing:
A. Early Classification:
a) Aristotle: Grouped plants into trees , shrubs and herbs based on their habit. He divided animals into Enaima and Anaima on the basis of presence and absence of RBC respectively.
b) Charaka who was considered as the father of Ayurveda listed 200 kinds of animals and 340 kinds of plants in his book 'Charak Samhita.
B. Artificial system of Classification
It is a system of classification which is based on the morphological characters. The earlier system of classification was given by Aristotle who classified on the basis of habit and habitat. Besides him, It was Theophrastus, Pliny, Bauhin, John Ray, Linnaeus who proposed the artificial system of classification of plants. This classification was based on the number and situation of stamens, styles, and stigmas rather than evolutionary relationships.
- According to Theophrastus the plants were classified on the basis of their habit and thereby placed them into herbs, shrubs and trees.
-Carlous Linnaeus: ( 1707-1778) was considered as the Father of Modern Taxonomy. He classified the plants exclusively on the basis of the nature and number of stamens and carpels.He called it as the Sexual system of classification or numeric system of classification. He classified plants into 24 classes, in which 23 were of flowering plants ( Phanerogamia) and 24 th class had flowerless plant ( Cryptogamia). He proposed classes monandria (1 stamen) , Diandria (2 stamens) , tri and polyandria (3 or more stamens).
The details of his classification was published in Genera Plantarum (1737). The 24 classes named by him were: Monandria, Diandria, Triandria, tetrandria, Pentandria, Hexandria, Heptandria, Octandria, Ennendria, Decandria, Dodecandria, Icosandria, Polyandria, Didynamia, Tetradynamia, Monadelphia, Diadelphia, Polyadelphia, Syngenesia, Gynandria, Monoecia, Dioecia, Polygamia, Cryptogamia.
The artificial system of classification had a number of drawbacks, namely;
a) Since the system was based on limited characters , hence, the diverse groups of plants and animals were placed into limited number of groups.
b) There were no natural relationship amongst the organisms.
c)Leads to heterogenous assemblage of unrelated organisms.
d) No natural or phylogenetic relationships were considered.
C. Natural System of Classification
This system is based on natural afinities of plants. It is also known as the horizontal sytem of classification or 2'D' system. Various taxonomic characters are used to group the organisms. It is based mainly on the morphological relationships realizing all the information at the time of collection of plants. Some of the natural systems are:
a) A.L. Jussieu (1686-1758) attempted to clasify the plants in his book Genera Planatarum. He considered the number of stamnes with respect to the ovary and number of cotyledons. He considered 15 classes of plants.. these classes were further divided into 100 orders which were equivalent to the present day families.
b) A.p..de Candollow in 1819, classified the plants in his book ' Theorie Elementaire de la Botanique' . Characteristics of Vascular tissue was used for the system of classification. On that basis two major groups were recognized namely; vasculares ( vascular plans with cotyledons) including the groups Pteridophyta, Gymnosperms, Angiosperms and Cellulares ( Plants without vacular bundles and cotyledons) including the groups Thalophyta and Bryophyta.
c) George Bentham (1800-1884) and Joseph Dalton Hooker (1817-1911) proposed their system of classification in Genera Planetarium (1883) . In this system the Gymnosperms have been given an equal rank as that of Dicotyledons and Monocotyledons. This system has been followed by most of the herbaria of the world.
Merits of Natural system of classification :
It establishes natural relationship amongst organisms
It places only related organisms in a group.
It brings out the phylogenetic relationships and indicates the possible origin of different taxa.
An outline classification of phanerogamia is given as below:
Class Dicotyledonae:
General characters:
Pentamerous flower, reticulate venation in leaves, two cotyledons in seed, vascular bundles open with cambium , secodary growth present , wood formation occurs.
It is divided into 3 subclasses:
Subclass 1: Polypetalae- petals free and separate
It has three series:
Series1: Thalamiflorae: Flower hypogynous , Stamens and Pistils many ( indefinite) , petals free. Distinct sepals are free from ovary. It has 6 orders.
Series 2: Disciflorae: Flower hypogynous , Calyx consists of free or united sepals . Petals free. A prominent cushion shaped disc is present below ovary. It has 4 orders.
Series 3: Calyciflorae: Flower perigynous or epigynous , calyx contains united sepals ( rarely free) . Ovary inferior. It ha 5 orders.
Sub class 2: Gamopetalae- Petals united or fused.
It has three series:
Series 1: Inferae – Flower epigynous, ovary inferior, stamens as many as corolla lobes or fewer. It has three orders.
Series 2: Heteromerae- Ovary usually superior , carpels mor than two. It has 3 orders.
Series 3: Bicarpellate: Ovary usually superior, two carpels ( rarely one or three). It has 4 orders.
Sub class 3: Monochlamydaeae- Flower incomplete , no distinction between calyx and corolla . The presence of perianth is there which is usually sepaloid and may be absent.
It is divided into 8 series:
Series 1: Curvembryeae- Embryo carved , generally one ovule in ovary and one in each locule.
Series 2: Multivulatae Aquaticae: Plants are aquatic , submerged herbs, syncarpous ovary.
Series 3: Multivulatae Terrestres: Plants are terrestrial, syncarpous ovary.
Series 4: Microembryae; Very minute or small embryo.
Series 5: Daphnales- Ovary with one carpel and one ovule.
Series 6: Achlamydosporeae: Ovary unilocular with one to three ovules. Ovary inferior.
Series7: Unisexual: Flower unisexual
Series 8: Ordines Anomali- Families having plants with anomalous ( abnormal) characters.
Class 2: Gymnospermae
Sex organs on cones , perianth absent , ovule naked ( found inside ovary ) , seeds are also naked haploid endosperm.
It has families -Gnetaceae, Coniferae, Cycadaceae.
Class 3: Monocotyledonae
Parallel venation in leaves , embryo with one cotyledon , flower usually trimerous, wood absent, no secondary growth.
It has seven series:
Series 1: Microspermae: Ovary inferior, seed minute
Series 2: Epigynae: Ovary inferior, seeds larger
Series 3: Coronarieae: Ovary superior, perianth coloured
Series 4: Calycineae: Ovary superior, perianth green
Series 5: Nudiflorae: Perianth absent, ovary superior
Series 6: Apocarpae: carpels free ( apocarpous)
Series7: Glumaceae: Flowers arranged in spikelets with bracts.Perianth reduced , bracts large and scaly.
In this classification class is like division , series is like class, cohort is like order and order is like family.
Merits of Bentham and Hooker System of Classification:
(i) It is practically useful. It is considered to be the most useful system in India.
(ii) In this system of classification Monocots have been considered to be more advanced as compared to Ranales which have been considred to be primitive.
Demerits of Bentham and Hooker System of Classification:
(i) Gymnosperms were plced between dicots and monocots
(ii) Many important floral characters have been neglected.
(iii) This does not take the phylogenetic system into consideration, it believes in fixity of species.
(iv) There is a distinct discrimination; Some closely related families have been put under different cohorts while unrelated families have been placed nearer.
(v) Advanced family like Orchidaceace have been considered as primitive.
Phylogenetic System:
The evolutionary history of a group of organisms is called phylogeny.The term was coined by Lamarck. According to this system plants were classified in order of their evolutionary and genetic affinities. In this the organisms belonging to the same taxa have been believed to have a common ancestor and may be represented in the form of a family tree which is known as Cladogram.
A.K Eichler modified Bentham and Hooker's sysyem by placing gymnosperms in the beginning. He has been cosidered as the pioneer in the phylogenetic system of classification.
Adolf Engler and Karl A.E. Prantl. are two German botanists, who adopted the phylogenetic system of classification.
Merits of Phylogenetic system:
The families are arranged according to increasing complexity of flowers.
Demerits of Phylogenetic system:
(i) Monocots were considered primitive to dicots.
(ii) According to this form , primitive forms have naked flowers, which is placed in the beginning. The more advanced families have distinct perianth while the highly evloved families have fuse perianth.
John Hutchison presented the phylogenetic classification in his book” Families of Flowering plants” in 1959.
According to Hutchinson's classification:
(i)The trees and shrubs have been considered to be more primitive than the herbs.
(ii) The dicots have been considered more primitive than the monocots
(iii) Polypetalous actinomorphs and solitary flowers have been considered more primitive.
The outline classification of Hutchinson's Classification is as follows:
Divisions include order which in turn includes families. The division does not include classes.
'Taxonomy without Phylogeny is bone without flesh' – was stated by Takhajan
Branches of Taxonomy:
1.Classical Taxonomy:
(i)It deals with employing all available information to classify organisms on the basis of their origin , evolution, affinities and variations.
2. Numerical taxonomy/ Phenetics/ Taximetrics/ Adansonian taxonomy
(a) Uses statistical methods for evaluating similarities and differences between species. All selected characters have been given equal importance. The comparisons have been made easier by the use of calculaing machine and computers.
(b) Dendrogram is family tree of organisms on the basis of numerical taxonomy.
3. Biosystematics:
It deals with variations within a species and its general evolution.
4. Cytotaxonomy/ Karyotaxonomy:
based on the cytological information on cell, chromosome number, their structure and behaviour, during meiosis.
5. Chemotaxonomy:
based on the chemical constituents of plants i.e. Betacyanin pigment in beet roots, raphides and cystolith, sequencing of DNA and chemical nature of proteins.
Taxonomy was divided into three parts by Turril:
(i) α taxonomy: based on gross morphological features including compilation of monographs and flora
(ii) β taxonomy: based on morphology and evidences from genetics, cytology, anatomy, physiology etc.
(iii)Ω taxonomy: It includes all microscopic and biochemical evidences.
Classification of Plant Kingdom
The major groups of Plant kingdom include:
a) Thallophyta
b) Bryophyta
c) Pteridophyta
d)Gymnosprms
e) Angiosperms
1. THALLOPHYTA- ALGAE
The thallophytes are polyphyletic group of non-mobile organisms traditionally described as relatively simple plants or lower plants with undifferentiated bodies (thalli)
General characters of algae:
1) Eukaryotic, autotrophic, chlorophyllous, cryptogamic, thallophytes.
2) They are aquatic forms, either fresh water or marine forms.
3) Available in many forms: Unicellular ( Chlamydomonas), In colonial form ( Volvox), palmelloid ( Tetraspora), dendroid ( Prsinocladius), filamentous unbranched ( Spirogyra) or branched ( Chladophora), heterotrichous ( Fritschiella, Coelochaete, Stigeoclonium), siphonaceous (Vaucheria), parenchymatous (Ulva)
4. The food is stored in the form of starch.
5.Reproduction:For aquatic organisms such as algae, dispersal and desiccation stresses are at a minimum.
(a) Vegetative reproduction;It takes place by fragmentation.
(b)Asexual reproduction : It takes place by zoospores, aplanospores, hypnospores, akinetes, palmella stage, autospores.
(c)Sexual Reproduction: Sex organs are unicellular or multicellular, with all fertile cells and non-jacketed. The embryonic stage is absent. There are three types of gamets namely (i) isogamous (ii) Anisogamous (iii) Oogamous. Sporic or Gametic or Zygotic meiosis occurs in the life cycle.
Algae was classified into 11 classes by F.E. Fritsch in his book titled “ Structure and Reproduction of the Algae” mainly on the basis of pigmentation , reserve food, flagellation, thallus structure, mode of reproduction and life cycles.
Whitaker included only Chlorophyceae ( green algae), Phaeeophyceae ( brown algae) and Rhodophyceae ( red algae) in algae under Kingdom Plantae.
( a) Green algae ( Chlorophyceae):
General Characteristics:
(i) Exist in mostly fresh water forms ( Spirogyra, Ulothrix, Chara, Chlamydomonas, Volvox ) and marine forms as well ( Acetabularia, Ulva)
(ii) Photosynthetic pigments are chlorophyll a , chlorophyll b and carotenoids.
(iii) Isokont flagellation
(iv) Thyllakoids are in group of 2-20 per lamella.
(v)Pyrenoides present.
Three types of life cycle occurs in the Green Algae:
(a) Haplontic Life Cycle: e.g. Ulothrix, Spirogyra, Chlamydomonas ( Zygotic meiosis occurs)
(b) Diplontic Life cycle e.g. Caulerpa ( gametic meiosis)
(c) Diplohaplontic life cycle e.g. Ulva, Cladophora. The haploid and diploid phases are well developed and multicellular. The isomorphic alternation of generation is found.
1.Chlamydomonas:
Chlamydomonas is microscopic, unicellular green plants (algae) which lives in fresh water. Typically their single-cell body is approximately spherical, about 0.02 mm across, with a cell wall surrounding the cytoplasm and a central nucleus.Two filaments of cytoplasm, flagella, extend from one end, and their whip-like lashings pull the chlamydomonas through the water and rotate it at the same time. A single, cup-shaped chloroplast occupies the greater part of the cell. In this chloroplast is a protein region called a pyrenoid, which is involved in starch production and is often surrounded by starch granules. The cell wall is made up of hydroxyproline (glycoprotein).Presence of neuromotor apparatus ) basal granules + paradesmos + rhizoplast + centrosome ). Two contractile vacuoles, single eye spot or stigma as photoreceptor organ are present.
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| Chlamydomonas |
Red snow is caused by hypnospores of Chlamydomonas nivalis. Haematochrome , a carotenoid pigment is present in them.
Bald spot: receptive, colourless spot of oogonium through which male gamete enters.
Reproduction:
Asexual reproduction by zoospore, aplanospore, hypnospores, and palmella stage.
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| Life cycle of chlamydomonas - A. Zygospore(n) B. Sporogenesis C. Asexual reproduction D. Sexual reproduction E. Meiosis F. Diploid zygote(2n) G. Conjugation of haploid isogametes H. Haploid daughter cells (n) I. Sporangium |
Asexual reproduction:
(i)By zoospore : Under favourable conditions
(ii)By Palmella stage: Formed in response to dessication conditions and toxic salts. The spores sre green , non-motile and are capable of growth and division.
(iii) By aplanospore ( thin walled spore ) or hypnospores ( thick walled spores). These are formed under drought conditions. e.g. Chlamydomonas caudata.
Sexual reproduction:
It is of the following types:
(i) isogamy ( fusion of similar gametes) e.g. Chlamydomonas debaryana ( homothallic) or Chlamydomonas reinhardii ( heterothallic).
(ii) Anisogamy ( fusion between a motile, smaller, male gamete and a motile larger morphologically dissimilar female gamete ) e.g. Chlamydomonas braunii.
(iii) Hologamy ( fusion of young cells ) e.g. Chlamydomonas media
(iv) Oogamy: ( fusion between a motile male amete and a non-motile female gamete ) e.g. Chlamydomonas coccifera.
2. Spirogyra
It is commonly called as summer alga or hair of princess or pond silk or water silk or pond scum ( due to mucilage covering found in stagnant water. .They are a free-floating filamentous form of green algae, commonly seen as bright green masses on the surfaces of freshwater ponds and ditches. It is a genus of green algae, belonging to the order Zygnematales. The name 'spirogyra' is derived from the spiral arrangement of chloroplast in its filament-like body. Spirogyra cells are cylindrical in shape and are connected end to end, forming a long, unbranched filament-like structure. The cell wall is made up of an outer layer of cellulose and an inner layer of pectin. The inner surface of the cell wall is lined with a thin layer of cytoplasm. The spiraled ribbon-shaped chloroplasts are embedded in the cytoplasm lining. The number of chloroplasts in each cell may vary from one to sixteen. Each chloroplast has several round bodies called 'pyrenoids', which are responsible for the production of starch. Each cell has a prominent nucleus in the center, suspended by thin strands of cytoplasm from the inner part of the cell wall. The cells are long and thin, and each spirogyra filament measures between 10 to 100 micrometer in width. Sometimes, these filaments have root-like structures, which help them attach themselves to the substratum.
Spirigyra adnata and Spirogyra jogensis are attached to the subsratum by basal cell called holdfast or hapteron.
Reproduction :
Spirogyra shows three kinds of reproduction namely: vegetative, asexual and sexual.
(i) Vegetative reproduction : By fragmentation.
(ii) Asexual reproduction :
a) By parthenogenesis or azygospores: e.g. Spirogyra varians, when placed in the sugar solution , develops parthenospores.
b) By akinetes: e.g. Spirogyra farlowi
c) By aplanospores
Sexual Reproduction:
It occurs by conjugation. Physiological anisogamous type.
Types of conjugation:
a) Scalarifirm conjugation: It is the most common type of conjugation. Occurs in heterothallic and homothallic species. Minimum two filaments are involved e.g. Spirogyra tuwensis.
b) Lateral conjugation: Two adjacent cells of same filament function as gametangia. e.g. Spirogyra affinis.
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| conjugation in spirogyra |
Economic importance of green algae:
(i) Codium and Ulva ( Sea lettuce) is used as salad or vegetable in Europen countries after drying and salting.
(ii) Chlorella pyrenoidosa ( space alga) is used by exobiologists for food , oxygen and disposal of CO2 and organic waste in prolonged space flight.
(iii) Cephaleuros virescence : It is parasitic green alga which causes red rust of tea disease.
Brown Algae ( Phaeophyceae):
General Characters:
(i) The members of this group are called brown algae due to their characteristic brown colour obtained from the pigment present fucoxanthin.
(ii) The brown algae are marine in nature exclusively found primarily in the coastal region. They are found in the cooler seas. Sargassum is a warm water form that occurs in the North Atlantic Ocean region and forms Sargasso sea.
(iii) The brown algae is never unicellular. Most of the brown algae are macroscopic except a few which are microscopic. The massive size algae are Laminaria (2-9 mts) Nereocystis (45 mts) ; Macrocystis (60-90 mts) . Because of their bulky appearance , thay are called giant kelps.
(iv) The body of a typical brown alga ( Laminaria) is differentiated into holdfast, stipe and lamina.In some large brown algae, certain cells are modified to form long filaments called trumpet hyphae. These carry food from lamina to the holdfast.
(v) The cell walls of brown algae are generally composed of twolayers -an inner cellulosic layer and an outer mucilaginous layer.The cellulosic walls are coveres by a colloidal covering called phycocolloids.
(vi) Alginic acid is an important component of the phycocollois and is comercially obtained from kelps. It has haemostatic properties and has been used in emergency transfusions in the treatment of shock. Sodium alginate has been used as a stabilizer in food industries; calcium alginate in plastics. Forms of alginic acid are used in textile, rubber and paint industries. It is used for making the ice creams smooth.
(vii) The cell of brown algae contain fucosan vescicles. The functions of which are not known.
(viii) The cells contain a pigment fucoxanthin in addition to chlorophyll a and c. Fucoxanthin dominates over the green colour of the chlorophyll , imparting brown colour to the algae.
(ix)The reserve food material in the algae is in the form of laminarin starch and mannitol.
(x) Asexual reproduction occurs by motile or non-motile spores formed inside large sized cells called sporangia which may be unicellular or multicellular.
(xi) Sexual reproduction takes place by the formation of flagellate gametes which are formed inside the gametangia.In some cases the female gamete is non- motile. The gametes may be isogametes, both similar) , or anisogametes ( both similar but female larger in size), or oogametes.
( female large non- motile, male motile , small)
Economic Importance of Brown algae:
(i) Fucus and Laminaria are rich source of Iodine.
(ii) Laminaria yields a food product which is rich in carbohydrate called Kombu and Alaria produces Sarumen in Japan.
(iii)Durvillea has antiworm properties.
Red algae( Rhodophyceae):
General Characters:
(i)The red colour of the red algae is because of the presence of r-phycocyanin and r-phycoerythrin.Mostly marine.
(ii)The thallus of red algae varies from being microscopic, unicellular to half a meter in length. These may be unicellular, filamentous, ribbon shaped or leaf like. Some of these secrete calcium carbonate over their walls and form coralline structures. Corallina , a red alga is the main producer in some coral reefs.
(iii) In deep oceans they acquire deeper color. Only the blue green light reaches the deep water. The pigments r-phycoerythrin in red alga captures light of available wavelength for the red lagae.
(iv) Some red algae are also parasitic in nature. e.g. Herveyella is parasitic on other red algae. The parasitic forms , however , are colourless.
(v) The cell wal contains cellulose and pectic material along with some polysaccharides called photocolloids , some of which might contain sulphur e.g. Agar. Agar is widely used to prepare solid food nedia for the growth of bacteria and fungi in the laboratory, although it has no food value for the bacteria and fungi. Human beings also use agar as a thickening and binding agent in various food products.Agar-agar is obtained commercially from algae Gelidium and Gracilaria.
(vi) Carageenin is a biochemical substance present in the cell walls of red algae which is used as thickening and binding agent in food products like pudding etc.
(vii) The cells appear in uninucleate or multinucleate forms with one or more plastids. That may be with or without pyerenoids. The food reserve lies in the form of Floridan starch and a soluble sugar fluoridodoside.
(viii) Asexual reproduction takes place with the help of non motile spores. Fragmentation is the common mode of reproduction, Although some of the red alga is able to regenerate the full plant from the severed holdfast.
(ix) The red alga exhibits highly advanced form of sexual reproduction. It is also oogamous. Flagellated gametes are absent in red algae. The male gametes are known as spermatia which are developed in the special type of structures called spermatangia while the female cells are known as carpogonia. The carpogonium is a flask shaped structure having a neck like trichogyne.
(x) Alternation of generation in haploid and diploid stages are seen to occur in many algae.
2.Bryophyta
General Characteristics:
1. They are found in moist and shady places i.e. Sciophytes. They usually grow during damp season , forming green carpets, on rocks, walls, tree trunks etc.
2. There are exceptions that is they also exist in aquatic forms: (i) Riccia fluitans, (ii) Ricciocarpus ntans (iii) Riella; Fontinalis saprophytic forms.: (i)Cryptothallus mirabiliis, (ii) Buxbaumia aphylla, and epiphytic form (i) Frullania.
3.The dominant phase or plant body is a free living gametophyte.
4.No vascular tissue in either generation. Root-like structures are rhizoids.
5.The rhizoids may be unicellular or multicellular.
6. The vegetative reproduction is common by fragmentation, tubers, gemmae, buds, adventitious, branches etc. Mitospores are not formed.
7. Sexorgans are multicellular and jacketed. They are of two types, male antheredium and female archegonium.
8. An external layer of water is essential for the swimming of male gametes and to reach the archegonia.
9. Fertilization produces an embryo iside the archegonium. The embryo grows into a sporophyte
10. The sporophyte is parasitic over the gametophyte.
11. The sporophyte of bryophytes is known as sporogonium. It produces haploid spores inside its capsule part while still being attached to the gametophyte.
12. On germination each spore produces a gametophyte either directly or through a juvenile filamentous stage called protonema.
13. The alternation of generation is either heteromorphic or heterologous.
Classification of Bryophyta
Bryophyta
Classes Hepaticopsida Anthoceropsida Bryopsida
(Liverworts) (Hornworts) (Mosses)
e.g. Riccia, Marchantia e.g. Anthoceros e.g. Funaria (cord moss)
Life cycle of Funaria Hygrometrica
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| Structure of Funaria Sporophyte |
Funaria is a radially symmetrical plant differentiated into stem, or central axis, leaves, or phylloides and rhizoides. The rhizoides are multicellular , branched, with oblique septa. It is monoecious and autoicous ( both sex organs are on the same plant but on different branches). The Antheredia are borne at the tips of the main axis and surrounded by perigonial leaves. Archegonial clusters are borne on lateral branch tip and are surrounded by perichaetial leaves. Both male and female gametangia are acrocarpous. Male gametes or sperms are elongated , biflagellate and has a curved body. The archegonium has 6-10 neck canal cells.
Diploid oospore develops into sporophyte. Mature sporogonium is differentiated into foot, seta and capsule. Foot is embedded in gametophytic plant body, meant for absorption of water , mineral salts and fixation. Seta is a narrow stalk which lifts the capsule in the air. Capsule is differentiated into three parts -apophysis, theca and operculum.
Apophysis contains assimilatory tissue, stomata with singular annular guard cell. Theca contains central sterile columella , a spore sac, air cavity and assimilatory tissue. Operculum is separated from theca by one celled elongated diaphragm. The annulus lies above the rim.
Peristomial teeth are 32, acellular, arranged in 2 rings of 16 each. The outer periosteum teeth are exostome, bear transverse thickening of cellulose, showing hygroscopic movement. Endostome or inner peristomel teeth are without cellulose thickening, acts as sieve and checks sudden dispersal of spore .
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| The two basic peristome types of mosses. A. Cross section of an embryonic sporophyte capsule. B. Nematodontous peristome (e.g., Polytrichum). C. Arthrodontous peristome (e.g., Funaria or Bryum). |
Some common names:
Some facts:
(i)Smallest bryophyte is Zoopsis
(ii) Largest bryophyte is Dawsonia
(iii) Largest archegonium in plant kingdom is of Funaria.
(iv)The term Bryophyta was coined by Robert Brawn (1864) but it was delimited in its form by Schimper(1879).
3. Pteridophyta
General characters:
(i)The term pteridophyta was coined by E.Haeckel for plants with feather like fronds.
(ii)They are the first group of tracheophytes. The plant body is sporophytic.Sporophyte plant body has true roots, stem and leaves with well developed vascular system.
(iii)Meiospores are formed inside sporangia. These sporangia are associated with leaves called sporophyll.
(iv)Most pteridophytes are homosporous; only a few show heterospory.Spores are produced in multicellular sporangia after meiosis in spore mother cells.
(v)The life-cycle shows distinct heteromorphic alternation of generations.
(vi)Diploid sporophyte generation is predominant.
(vii)Asexual reproduction takes place by spores.
(viii)Gametophyte is haploid, multicellular, green and an independent structure.
(ix)Sex organs, antheridia and archegonia are multicellular.
(x)Antherozoids (sperms) are spirally coiled and multi flagellate.
(xi)Opening of sex organs and transfer of male gametes to archegonium for fertilization are dependent on water. Further, fertilization takes place inside the archegonium.
(xii)Vascular tissues are present. They are of two types, xylem and phloem. In xylem true vessels are absent. In phloem , companion clls are absent and sieve cells are present.
(xiii)Sporangium development is of two types:
(a) Leptosporangiate: When sporangium develops from single superficial cell. e.g. Pteris, Dryopteris, Adiantum.
(b) Eusporangiate: Sporangium develops from single superficial cells.e.g. Selaginella , Equisetum.
(xiv) Sex organs are multicellular and jacketed . Antheredia are reduced.Archegonia are partially embedded.
(xv)The embryo stage is present and the embryogeny is of two types:
Development of embryo :
(a)Holoblastic- When the entire zygote is involved in embryonic development.e.g. Ferns.
(b)Meroblastic – when the part of zygote is involved in embryonic development e.g. Selaginella
Some common examples of microphyllous pteridophytes (i.e., poorly developed leaves) are club mosses (Lycopodium sp.), and whisk ferns (Psilotum sp.). Examples of megaphyllous (large-leafed) pteridophytes are the ferns Nephrolepis, Osmunda, Pteris, and Salvinia.
The steeler theory was proposed by VanTeigham and Douliot.
Types of Steles
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| Types of Steles |
A. Simple protostele
A'. Actinostele
A''. Plectostele
B. Ectophloic siphonostele
B'. Amphiphloic siphonostele (solenostele)
B''. Dictyostele
C. Eustele
D. Atactostele, the only stele type not found in the ferns
Siphonostele : It has evolved from the protostele. In siphonostele, pith is present in the center of the xylem cylinder. The phloem is external to xylem.
Solenostele : A Cbroken at one point at a time due to the non-overlapping leaf gaps is called solenostele
Dictyostele : Siphonostele in which many overlapping leaf gaps occur at the same level is called a dictyostele, or dissected siphonostele. In a transverse section it appears broken into many smaller or larger arcs. Each arc is known as a merestele (e.g. fern rhizome). Each meristele is completely and independently surrounded by the pericycle and the endodermis. This is the most highly- evolved stele type in Pteridophyta.
Eustele : The characteristic stele present in dicot and gymnosperm stems is called a eustele (i.e." true" stele). It is also a dissected siphonostele in which the vascular cylinder is dissected into separate vascular bundles arranged in a ring. The entire ring of vascular bundles is surrounded by the pericycle and the endodermis.
Atactostele : This is a complex type of stele in which numerous vascular bundles remain irregularly scattered in the ground tissue (atactos means without any order). Atactostele is a characteristic of monocot stems. Here, due to the scattered vascular bundles, the cortex and stele are not demarcated. Similarly, the endodermis and the pericycle are not differentiated.
Life Cycle of Selaginella:
The plant body is an evergreen sporophyte. It is differentiated into stem , leaves and roots. The roots develop at the tips of rhizophores.
Salient features:
1. Plant body is an evergreen sporophyte. It is differentiated into stem , leaves and roots. The roots often develop at the tips of special structures called rhizopores.
2. Vegetative growth is by fragmentation , bulbils and tubers. The function of bulbils and tubers help in perennation.
3.Sporangia develop in the axil of fertile leaves or sporophylls at the tips of small branches called spikes. There are two types of sporangia, micro and megasporangia.
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| Selaginella Kraussiana- |
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| Life cycle of Selaginella |
4. Each microsporangium produces a large number of small haploid microspores . A mgasporangium develops only four haploid megaspores. Growth of the gametophyts is precocious.
5..The plants exhibit dorsiventral or radial symmetry. All the vegetative parts contain vascular tissues, which are organized in steele.
6.The xylem mainly consists of traceids and xylem parenchyma . The vessels are generally absent but the primitive types are found in Selaginella, Equsetum, Pteridium.
7.The phloem consists of sieve- tube and phloem parenchyma. The companion cells are absent.
8. Microspore produces an endosporic 13 celled male gametophyte. This gametophyte has one prothallial cell and jacket cells and 4 androgonial cells. The androgonial cells give rise to 128-256 androcytes or sperm mother cells. A sperm cell gives rise to a biflagellate sperm.
9. The megaspore produces exosporic female gametophyte. The female gametophyte contains an exposed generative apical cuushion and storage tissue as well. A diaphragm separates the two. The apical cushion produces archegonia and rhizoids. Each archegonia has a single female gamete or oosphere. Fertilization requires external water for the swimming of sperm. Diploid oospore is produced.
10.Oospore divides to produce a suspensor and embryo. The development of embryo is meroblastic. Suspensor pushes the embryo into the food laden storage tissue. The embryo has a foot for absorbing the nourishment, moreover, it also has a shoot tip and a root tip. These two elongate to produce an independent sporophytic plant body.
11. Selaginella shows two distinct generations , i.e. The sporophytic and the gametophytic, one producing the other. Morphologically they differ from each other. The phenomenon is termed as hteromorphic or heterologous alternation of generation.
12. Under dry conditions , the xerophytic species of Selaginella roll into brown balls. The phenomenon is known as cespitose habit. They may remain uprooted under this condition. But during moist conditions these brown balls become green and unroll again under moist conditions. Therefore, these plants are calles aas resurrection plants. e.g. Selaginella lepidophylla,
Selaginella bryopteris.
13. Plant body of Selaginella chrysocaulos and Selaginella selaginoides is erect. The leaves are isophyllous and arranged in two rows. The plant body of Selaginella is prostrate. The leaves of this are anisophyllous or dimorphic and arranged in four rows.
14. The stem in Selaginella is distelic. Rarely stem is monostelic.
15. Bower and Goebel named rhizophore of Selaginella as an organ sui-generis, i.e. Bearing the characteristics of both stem and root but independent in origin.
16. The mucilage oozing out of the neck of the archegonium in Selaginella and Fern contains malic acid. The neck of archegonium in Selaginella and fern contains only one neck canal cell.
17. Selaginella rupestris shows seed habit.
Ferns (Pteridophytes)
1) The plant body is a sporophyte. It is differentiated into true stem, leaves and roots.
2) Most of the ferns have underground rhizome. Some are called tree ferns.e.g. Cyathea, Celotia.
3) The venation is furcate type in which the veins branch dichotomously without forming interconnections.
4) The younger parts of stem, young leaves, petiole and rachis of mature leaves possess hairs or scales called ramenta. These protect them from mechanical injury and dessication.
5) Young leaves show circinate ptyxis , that is they have a coiled appearance. This coiling protects the growing tip which comes to lie in the centre.
6) Sporangia occurs on the leaves in clusters called sori . The fertile leaves are known as sporophylls. A sorus is covered by a flap like outgrowth from its surface ( true indusium, e.g. Dryopteris) or turned margin of the sporophyll ( false indusium, e.g. Adiantum)]
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| Fern |
Life cycle of Dryopteris:
The salient ffeatures are as follows:
a) It is found in moist shady places. Located in tropical and subtroical areas.The plant body is perennial. They are independent, living , evergreen . The sporophyte has vascular tissues. The body is differentiated into stem , roots and leaves. The roots are adventitious. Stem is an underground dark brown rhizome.The large aerial leaves or fronds are incompletely bipinnate compound leaf. The young leaves show circinate ptyxis. Persistent leaf bases of the dead leaves are found in older parts of rhizome.
In Dryopteris a leaflet has a single midrib giving rise to lateral veins showing dichotomous divisions. The young leaves , young parts of rhizome , petiole, and rachis of mature leaves are covered over by brown to black scales called paleae or ramenta.
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| Life cycle of Dryopteris: |
(b) Reproduction:
The fern reproduces vegetatively by fragmentation of rhizome and develops adventitious buds. In Dryopteris the adventitious bud present at the leaf base separates and grows into a new plant. As the leaf bud touches the soil, a new plant develops. Cosequently the fern spreads over a large area. An example is Adiantum caudatum, which is also termed as the walking fern, and maiden hair fern.
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| Reproduction in Fern |
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| Dryopteris: T.S sorus |
A sorus consists of parenchymatous cushion or placenta. The placenta bears a number of stalked biconvex sporangia. In each sporangium there is a single layered jacket that encloses 12-16 diploid spore mother cells. A marginal row of jacket cells are differntially thickened to form annulus. The remainng marginal cells constitute stomium. The diploid spore mother cells divide meiotically to form haploid spores. As the spores mature the indusium shrivels. The exposed sporangia dehisce in the region of stomium due to differential contraction of annulus. The spores are dispersed by air currents.
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| Dryopteris - sporangia |
As the spores fall on the suitable soil , each spore germinates and forms thalloid gametophyte called prothallus. It is a cordate, green and the structure is flat. Prothallus bears antheridia and archegonia at the ventral surface
The antheridium has 3 celled jacket and 32 mother cells. The sperms are multiflagellate and spirally twisted. The archegonium is flask shaped and has a single binucleate neck canal cell, single ventral canal cell and an oosphere. Sperms are attracted to the opened archegonia by malic acid present in their mucilage. Diploid oospore gives rise to an embryo which grows in size to form the fern plant.
Gymnosperms
(i)Gymnosperms are seed plants that do not produce flowers. The term gymnosperm means "naked seed." However, usually when the seeds of gymnosperms are immature they are enclosed within and protected by modified leaves or a cone.
(ii)All gymnosperms are perennial woody plants forming either bushes or trees. Some are very large and live for about a thosand years. e.g. Sequola sempervirens.
(iii)Leaves are generally dimorphic , foliage and scaly types.
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| Pinus ; a gymnosperm. |
(iv)There are four groups of gymnosperms living today—Coniferophyta, Cycadophyta, Ginkgophyta, and Gnetophyta.
(v) All gymnosperms produce at least some secondary growth, . The most abundant product of secondary growth is the secondary xylem (xylem is the water-conducting tissue of plants), or wood
(vi)The foliage leaves do not have lateral veins. Transfusion tissue occurs internally for lateral transport.
(vii) The wood is homoxylous but Gnetales bear vessels in xylem. e.g. Ephedra, Gnetum, Welwitschia.
(viii) Types of wood:
(a) Manoxylic : Soft wood, vaculat tissues with medullary rays, commercially less important e.g. Cycas.
(b) Pycnoxylic: Compact wood without or with narrow medullary rays, comercially more important e.g Pinus.
(c) Monoxylic: With single persistant cambium rings and bundles. e.g. Cycas.
(d) Polyxylic: With many persistant cambium rings and bundles e.g.Cycas
(ix) Flowers are absent. There are two types of sporophylls, microsporophylls and megasporophylls.
(x) The two types of sporophylls are usually aggregated to form distinct cones or strobilli, pollen cones, ( male cones) and seed cones ( female cones).
(xi) Seeds do not occur inside a fruit. They are naked or lie exposed on the surface of megasporophylls.
(xii) Ovule lie exposed on the megasporophyll. Ovules are unitegmic and orthotropous.
(xiii) Pollination is direct as stigma is absent and the pollen grains directly reach the micropylar ends of ovules. Pollination is usually accomplished by wind ( anemophily).
(xiv) Male gametophyte produces only two male gametes or sperms. Generally only one is functional.
(xv) External water is not required as a medium for transport of male gametes. A polen tube is formed by the male gametophyte for affecting fertilization.
(xvi) Seeds contain a food laden tissue for future growth of embryo into seedling.
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| Life Cycle of Pinus: |
Pinus is a coniferous gymnosperm having pyramidal or excurrent shape like a christmas tree. Sporophytic plant body divided in stem, leaves and roots. Stem branches are of two types , long and dwarf. The dwarf branches have 1-5 needle - like foliage leaves which are surrounded by a sheath of scale leaves.
Number of needles are 1,2,3,4 and 5 in Pinus monophylla, Pinus sylvestris, Pinus roxburghi, P. quadrifolia, and Pinus wallichiana respectively. The root system is tap root, with long horizontal types. The mycorrhizal roots lack root hairs and root cap; and they occur near soil surface.
Vegetative reproduction is absent. Pinus is monoecious and develops into clusters of shortly stalked male cones subterminally on the lower branches and female cones in circle of 2-6 on upper long branches.
Male cone has a short stalk, a central axis and a number of spirally arranged microsporophylls. It bears two oblong , parallel microsporangia on its lower surface. In microsporangium the diploid microspore mother cells undergo meiosis and form haploid microspores or pollen grains.At maturity the pollen grains are released from the male cones and dispersed by air currents. Pollen grains have two prothallial cell, a generative cell and a tube cell. They form yellow clouds in the pine forests. A pollen grain has two air sacs or wings for making it light.
The female or seed cones develop in groups 2-6 on upper long branches of the tree. Each female cone has a long stalk and a central axis on which are borne a number of spirally arranged paired scales. The lower pair is called bract scale while the upper scale is ovuliferous scale or megasporophyll. The ovuliferous scale bears two ovules towards the basal region on the upper side. The ovule consists of a 3- layered integument witha wide micropyle and nucellus. A megaspore mother cell differentiates in the middle of nucellus.
4 haploid megaspores are formed by meiosis, but only one survives. The functional megaspore gives rise to female gametophyte. The female gametophyte bears 1-8 archegonia. An archegonium has a short neck and broad venter. Neck canal cell is absent. The venter canal is ephemeral. The oospore is contained in the venter.
The female cones open when they are ready to pollinate. The pollination is anemophilous i.e. By air. And direct. The pollen grains pass into the opened micropyle and rest on the top of the nucellus. The micropyle of each ovule contain a mucilage or pollination drop for catching the pollen. The germination takes place and pollen tube is formed but further growth is arrested due to oncomung winter season. In the spring of next year the fertilization takes place i.e 13 months after the pollination. The pollen tube grows and pierces the archegonium . The male gamete fuses with the female gamete to form a diploid zygote. This oospore in turn produces an embryo while the ovule matures into a seed. A part of the upper surface of the ovuliferous scale is peeled off along the seed to form a wing. A female cone takes 26 months to be mature . It then opens to release winged seeds which are dispersed into the air. On falling onto a soil each seed gives rise to a new plant.
Some facts about Pinus:
i) The number of cotyledons in Pinus range from 3-18
ii) The proembryo has 4 tiers i.e. The basal embryo tier, suspenser tier, rosette air, and upper tier.
Iii) Resin is collected by injuring Pinus. It is a semifliud secrested by special tubes. It solidifies on exposure to air, thereby plugging the places of injury. It acts as an antiseptic and commercially distilled to obtain turpentine and resin. The resin is used in water proofing, sealing joints and preparation of writing paper. Turpentine is used as solvent in paints , polishes and wax.
Angiosperms:
They are the flowering plants. These are the most advanced plants characterized by the presence of flower , covered ovules and seeds. They comprise the largest group in the plant kingdom. Present in all kinds of habitat and have gone through evolution since the cretaceous period. Angiosperms include hydrophytes, xerophytes, epiphytes, parasitic, saprophytic , insectivorous, symbiotic and mangrove kinds.
Characteristic features of Angiosperms:
(i) Flowers are present along with the sex organs.
(ii) Ovules covered and placed within the ovary.
(iii) The carpel receives pollen grains in its stigma.
(iv) Syngamy is typical of angiosperms
(v) A triploid endosperm is formed after fertilization.
(vi) Xylem and Phloem contain vessels and companion cells respectively.
(vii) The fertilized ovum ripen into seeds and the seeds are covered by fruits. The fruit is technically considered to be a ripened ovary. These fruits protect the seeds and help in their dispersal.
(viii) Xylem contains vessels and Phloem contains sieve tubes as well as companion cells.
(ix) A gametophyte can be haploid or diploid but always produces gametes.
(x)The monocots grow in length and not in width. They produce new leaves and flowers.
(xi) Dicots have an indefinite growth and new roots, shoots leaves, bark, and wood are formed every year.
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| Flower |
(xi)Petals are attractive and showy and attracts insects and other pollinators.
(xii) The pollination occurs by animal insects, worms, birds, bats and at times humans also.The insects accomplished pollination is termed as entomophily.
(xiii) The angiosperms are divided into two subgroups:
a)Dicots :They are the flowering plants characterized by the presence of two cotyledons in the seed, with reticulate venation in leaves, concentric tissue in the stem with open vascular bundles arranged in a ring, penta or tetramerous flowers.
b) Monocots: They are flowering plants which are characterized by the presence of a single cotyledon in the seed. The venation is of the paralel kind ie the leaves , with scattered closed type of vascular bundles in the stem and flowers are trimerous e.g. Banana, cereals, palm, grasses, bamboo, orchids etc.
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| Life cycle of Angiosperm |
Difference between various plant groups
Llife Cycle and Alternation of Generation
The haploid-diploid life cycle is the most complex life cycle and thus has lots of variation. It is also the most common life cycle among plants since all land plants, the vascular plants and the bryophytes, are haploid-diploid. An alternation of generations defines the haploid-diploid, or 1n-2n, life cycle. This occurs when a multicellular 2n sporophyte (SPT) phase alternates with a multicellular 1n gametophyte(GPT) phase.
In plants, the alternation involves alternating generations of haploid and diploid organisms. Often one of these generations is the dominant form of the organism, and the other generation is nutritionally dependent upon it or just grows as a smaller plant. For example, in mosses and liverworts, the haploid phase is the large, familiar form of the plant. The diploid phase is smaller and grows upon the haploid phase. In angiosperms, however, the diploid phase of the organism is large and independent, while the haploid phase is reduced to the pollen grain and the eight-celled female gametophyte located in the ovule.
Types of Life cycle or patterns of Alternation of Generation:
There are three main types of life cycle. These three types of cycles feature alternating haploid (n) and diploid (2n) phases.The haploid organism becomes diploid through fertilization, with joining of gametes. This results in a diploid zygote. To return to a haploid stage, meiosis must occur.
The cycles differ in the product of meiosis, and whether mitosis (growth) occurs. Zygotic and gametic meiosis have one mitotic stage and form during the n phase in zygotic meiosis and during the 2n phase in gametic meiosis. Therefore, zygotic and gametic meiosis are collectively term haplobiontic (single meiosis per phase). Sporic meiosis, on the other hand, has two meiosis events (diplobiontic): one in each phase.
They are as folows:
a) Haplontic Life cycle:It is characterized by the dominance of haplophase. The plant body is a gametophyte and independent. The sporophyte is dependent on gametophyte and is not free living The major part of life is gametophytic. e.g. Chlamydomonas, Ulothrix, Spirogyra
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b)Diplontic: The diplophase is dominant here. The main plant body is a sporophyte , being independent and free living. The gametophytes are extremely reduced and are dependent physically as well as nutritionally on te sporophyte. The major part of the life cycle is a sporophyte. e.g all gymnosperms and angiosperms; diatoms, some brown algae i.e Fucus and Sargassum.
c)Diplo- haplontic life cycle: Characterized by the existence of sporophyte as well as gametophyte. Both of them are photosynthetic and free living. The phases diplophase and haplophase are equal. If the sporophyte and gametophyte are morphologically different then the life cycle is Diplo-haplontic -heteromorphic type. e.g. All Pteridophytes; all bryophytes, some algae and Kelps. When the life cycle is morphologically identical then the life cycle is termed as Diplo-haplontic -isomorphic e.g. Green algae i.e Ulva, Cladophora etc.
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Very well done. Useful for UG students. May I use your images for teaching purpose? Thank You! Rajendra Shinde
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