3. Kingdom Plantae –
Part 01 - Division : Thallophyta
Kingdom plantae :
Kingdom Plantae is further classified on the basis of characteristics like -
absence or presence of seeds
vascular tissues
differentiation of plant body, etc.
Phanerogams
Phanerogams are commonly called seed producing plants.
They produce special reproductive structures that are visible (Phaneros – visible)
Cryptogams :
Cryptogams are spore producing plants and do not produce seeds and flowers.
They reproduce sexually by gametes but sex organs are concealed (kryptos : hidden, gamos : marriage).
Classification of Kingdom Plantae :
Salient features of major plant groups under Cryptogams :
A. Division : Thallophyta -
Members are mostly aquatic, few grow on other plants as epiphytes.
Some grow symbiotically and epizoic i.e. growing or living non-parasitically on the exterior of living organisms.
Aquatic algae grow in marine or fresh water.
Most of them are free living while some are symbiotic.
Plant body is thalloid i.e. undifferentiated into root, stem and leaves.
They may be small, unicellular, microscopic like Chlorella (nonmotile),Chlamydomonas (motile).
They can be multicellular, unbranched, filamentous like Spirogyra or branched, filamentous like Chara.
Sargassum, a huge macroscopic sea weed which measures more than 60 meters in length is also an alga.
The algal cell wall contains either polysacchrides like cellulose / glucose or a verity of proteins or both.
Reserve food is in the form of starch and its other forms.
Reprocuction takes place by vegetative asexual and sexual way.
The life cycle shows phenomenon of alternation of generation, dominant haploid and reduced diploid phases.
classification of Algae [as per its pigments like chlorophyll, xanthophyllsand phycobilin.]
OR
Types of algae :-
Chlorophyceae
Phaeophyceae
Rhodophyceae
1. Chlorophyceae (green algae) :
These are mostly fresh water (few brackish water and marine).
Plant body is unicellular, colonial,
filamentous.
Cell wall contains cellulose.
Chloroplasts are of various shapes like discoid, plate-like, reticulate, cup-shaped, ribbon-shaped or spiral with chlorophyll a and b.
The stored food is in the form of starch.
Pyrenoids are located on Chloroplast.
Members are rich in protein, so used as food; used even by space travellers.
e.g. Chlorella. Chlamydomonas, Spirogyra, Chara, Volvox, Ulothrix etc.
2. Phaeophyceae (Brown algae) :
Plant body : Mostly marine, rarely fresh water.
Simple branched / filamentous (e.g. Ectocarpus) / profusely branched (Petalonia).
Cell wall has cellulose, fucans and algin.
Photosynthetic pigments like chlorophyll-a, -c and fucoxanthin are present.
Mannitol, laminarin and starch are stored food materials.
Body is usually differentiated into holdfast, stalk called stipe and leaf-like photosynthetic organ called frond.
Many species of marine algae are used as food.
e.g. Porphyra, Laminaria, Sargassum.
Some species are used for production of hydrocolloids. e.g. Ectocarpus, Fucus, etc.
3. Rhodophyceae (Red algae) :
Plant body These are found in marine as well as fresh water on the surface, deep sea and brakish water.
Plant body is thalloid.
Cells contain chlorophyll a, d and phycoerythrin.
Cell wall is made up of cellulose and pectin glued with other carbohydrates.
Stored food is in the form of Floridean starch.
Commercially important agar-agar which is used as solidifying agent in tissue culture medium is obtained from red algae.
e.g. Chondrus, Batrachospermum Porphyra, Gelidium , Gracillaria, Polysiphonia, etc.
Do u know ?
Brown algae- kelps may grow up to 100 meters in height.
Part 02 - Bryophyta
Bryophyta (Bryon : moss ; phyton : plant) :
Bryophytes are mostly terrestrial plants.
They are found in moist shady places. But they need water for fertilization and completion of their life cycle. Hence they are called ‘amphibious plants’.
They include approximately 960 genera and about 25,000 species.
Life cycle of Bryophytes shows sporophytic and gametophytic stages.
Vegetative plant body is thalloid or leafy which represents gametophytic generation.
Spore producing capsule represents sporophytic generation.
Bryophytes have root-like structures called rhizoids.
Rhizoids are unicellular in liverworts while multicellular in mosses.
Rhizoids absorb water and minerals and also help in fixation of thallus on the substratum.
Bryophytes are divided into two groups :
liverworts and
mosses.
1. Liverworts (Hepaticeae) :
These are lower members of Bryophyta.
These are primitive group of Bryophytes.
Gametophyte possesses flat plant body called thallus.
The thallus is green, dorsiventral, prostrate with unicellular rhizoids.
e.g. Riccia, Marchantia.
Hornworts (Anthocerotae) -
These member possess flattened thallus.
The thallus produces horny structures which are called sporophytes hence the name hornworts. e.g. Anthoceros.
2. Mosses (Musci) :
These are advanced members of Bryophyta which possess erect plant body.
Gametophytic phase of the life cycle includes two stages namely-
protonema stage and
leafy stage.
Protonema stage :
The protonema is prostrate green, branched and filamentous (it is also called juvenile gametophyte).
It bears many buds.
Leafy stage is produced from each bud. Thus protonema helps in the vegetative propagation.
Leafy stage :
The leafy stage has erect, slender stem like (Cauloid) main axis bearing spiral leaf like structures (Phylloid).
It is fixed in soil by multicellular branched rhizoids.
This stage bears sex organs.
Vegetative reproduction takes place by fragmentation and budding in secondary protonema.
e.g. Funaria, olytrichum, Sphagnum , etc.
Economic importance of mosses -
Some mosses provide food for herbivorous mammals, birds, etc.
Species of Sphagnum, a moss; provides peat used as fuel.
Mosses are also used as packing material for transport of living materials because they have significant water holding capacity.
Just like lichens, mosses are the first living beings to grow on rocks.
They decompose rocks to form soil and make them suitable for growth of higher plants.
Dense layers of mosses help in prevention of soil erosion, thus act as soil binders.
Part 03 - Pteridophyta
Pteridophyta (Pteron : feather, phyton : plant ) :
Evolutionarily, Pteridophytes are the first vascular and true land plants. Hence considered as the first successful terrestrial plants with true roots, stem and leaves.
These plants have a primitive conducting system and they are the only Cryptogams with vascular tissues.
The late Paleozoic era is regarded as the age of Pteridophytes.
The group has about 400 genera and 11,000 species.
The plants consist of pinnate (feather like) leaves.
Leaves may be small called microphylls (e.g. Selaginella) or large called macrophylls (e.g. Nephrolepis / fern).
Pteridophytes grow in moist and shady places.
Pteridophytes show sporophytic and gametophytic stages in life cycle.
e.g. Ferns, Horsetail.
Some are aquatic (Azolla, Marsilea), xerophytic (Equisetum) and epiphytic (Lycopodium).
Pteriodphytes show heteromorphic alternation of generations in which the sporophyte is diploid, dominant, autotrophic and independent.
It is differentiated into root, stem and leaves.
The primary root is short lived and soon replaced by adventitious roots while the stem may be aerial or underground.
Leaves may be -
scaly - Equisetum
simple and sessile - Lycopodium or
large and pinnately compound - Nephrolepis / Ferns.
In these members Xylem consists of only tracheids and Phloem consists of only sieve cells.
Secondary growth is not seen in Pteridophytes due to absence of cambium.
Pteridophytes are classified as -
Psilopsida- Psilotum
Lycopsida - Selaginella and Lycopodium
Sphenopsida - Equiesetum) and
Pteropsida - Dryopteris, Pteris and Adiantum)
Economic importance -
Pteridophytes are Used for medicinal purpose and as soil binders.
Many varieties are grown as ornamental plants.
Part 04 - Gymnospermae
Salient features of major plant groups under Phanerogams
A. Gymnospermae (Gymnos : naked, sperma : seed) :-
There are about 70 genera and 1000 living species of Gymnosperms in world.
In India it is represented by 16 genera and 53 species.
Most of the Gymnosperms are evergreen, shrubs or woody trees.
These are primitive group of flowering plants producing naked seeds.
Seeds are not covered by fruit i.e. ovary.
They are vascular plants having Xylem with tracheids and Phloem with sieve cells.
The plant body is sporophyte.
It is differentiated into root, stem and leaves.
The root system is tap root type.
In some, roots form symbiotic association with other life forms.
Coralloid roots of Cycas show association with blue green algae and roots of Pinus show association with endophytic fungi called mycorrhizae.
In Gymnosperms, stem is mostly erect, aerial, solid and cylindrical.
Secondary growth is seen in Gymnosperms due to presence of cambium.
In Cycas it is usually unbranched, while in conifers it is branched.
The leaves are diamorphic.
The foliage leaves are green, simple needle like or pinnately compound, where as scale leaves are small, membranous and brown.
Spores are produced by microsporophyll (Male) and megasporophyll (Female).
Economic importance -
Cycas is grown as ornamental plant.
Pinus is used as source of pine wood, turpentine oil and pine resin.
Do u know?
Gymnosperms like Ginkgo biloba is called living fossil.
It is because the plant is found in living as well as fossil form and the number of fossil forms is much more than the living forms.
Gymnosperms vary in their size.
e.g. Sequoia sempervirens is the tallest living plant in the world. It is commonly called coast red wood of California. The height of the plant is about 366 feet. Taxodium mucronatum has agirth of about 125 feet.
Zamia pygmaea is thesmallest Gymnosperms and is about 25 cmonly.
Part 05 - Angiospermae
Angiospermae (Angios : enclosed :vessel, Sperma : seed) :
Angiosperms are the most advanced group of flowering plants.
In these plants the seeds are enclosed within the fruit i.e. ovary.
Angiosperms is a group of highly evolved plants, primarily adapted to terrestrial habitat.
They vary in size.
Angiosperms show heteromorphic alternation of generation in which the sporophyte is diploid, dominant, autotrophic and independent.
The gametophytes (male orfemale) are recessive, haploid and dependenton the sporophyte.
Angiosperms are heterosporous.
Microspores (commonly called pollens) are formed in microsporangia (or anthers).
They develop in highly specialized microsporophyll or stamens while megaspores are formed in megasporangia (or ovules) borne on highly specialized megasporophyll called carpel.
Besides the essential whorls of microsporophylls (Androecium) and megasporophylls (Gynoecium) there are accessory whorls namely calyx (sepals) and corolla (petals) arranged together to form flowers.
Do u know ?
Wolffia is the smallest Angiosperm, 1mm in size and Eucalyptus grows to over 100 meters.
Classificaion of Angiosperms :
Dicotyledonae
Monocotyledonae
1. Dicotyledonae :
These plants have two cotyledons in their embryo.
They have a tap root system and the stem is branched.
Leaves show reticulate venation while the flowers show tetra or pentamerous symmetry.
Vascular bundles are conjoint, collateral and open type.
Cambium is present between Xylem and Phloem for secondary growth.
In Dicots secondary growth is commonly found.
e.g. Helianthus annus (sunflower), Hibiscus rosa-sinensis (China rose).
2. Monocotyledonae :
These plants have single cotyledon in their embryo.
They have adventitious root system and stem is rarely branched.
Leaves generally have sheathing leaf base and parallel venation while the flowers are generally trimerous.
The vascular bundles are conjoint, collateral and closed type.
In Monocots, except few plants secondary growth is absent.
e.g. Zea mays (Maize), Sorghum vulgare (Jawar).
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Part 06 - Plant life cycle and alternation of generations
Plant life cycle and alternation of generations:
Life cycle of a plant includes two phases or distinct generations namely -
sporophyte (diploid : 2n) and
gametophyte (haploid : n).
Some special diploid cells of sporophyte divide by meiosis to produce haploid cells.
These haploid cells divide mitotically to give rise to gametophyte.
The gametophyte produces male and female gametes which fuse during fertilization to produce diploid zygote.
It divides by mitosis to form diploid sporophyte.
The sporophytic and gametophytic generations generally occur alternately in the life cycle of a plant. This phenomenon is called alternation of generations.
Distinct alternation of these two generations is observed in Bryophytes and Pteridophytes.
In Gymnosperms and Angiosperms, gametophyte is much reduced and exists within sporophyte.
In algae, based upon the nature of dominant phase in life cycle, it is called haplontic, diplontic or haplodiplontic life cycle.
In Bryophytes haploid gametophyte is dominant.
It is photosynthetic, independent thalloid or erect phase.
Sporophyte is short lived, multicellular and depends totally or partially on gametophyte for nutrition and anchorage.
Whereas in Pteridophytes, sporophyte is dominant, independent and vascular plant body.
Haploid multicellular gametophyte is generally autotrophic and short lived.
It alternates with Sporophyte.
Diplontic :
Here mitotic divisions occurs only in diploid cells.
Gametes formed through meiosis are haploid in nature.
The diploid zygote divide mitotically.
In this process production of multicellular diploid organism or in the production of many diploid single cells takes place.
E.g. Animals.
Haplontic :
Here mitosis occurs in haploid cells.
It results in the formation of single haploid cells or a multicellular haploid organism.
These forms produce the gametes through mitosis.
Zygote is formed After fertilization.
This cell is the only diploid cell in the entire life cycle of the organism. Thus the same zygotic cell later undergoes meiosis.
E.g. Some Algae and Fungi.
Haplo-diplontic :
Here mitosis occur in both diploid and haploid cells.
These organisms undergo through a phase in which they are multicellular and haploid (the gametophyte), and a phase in which they are multicellular and diploid (the sporophyte).
E.g. Land plants and in many algae.
