Artificial System of classification:-
This system used only gross superficial morphological characterizes such as habit, color, no. & shapes of leaves etc. They separated the closely related species.
Natural classification System:-
Given by George Bentham & Joseph Dalton Hook.
It considers both external & internal features like anatomy, ultrastructure, embryology & phytochemistry.
Evolutionary basis is neglected.
Phylogenetic classification System:-
It is based on evolutionary relationships among organisms.
They use information from various sources to solve problems of classification; such information becomes more important in the absence of supporting fossil evidence.
But, this system is not helpful in plant identification.
Types of Taxonomies:-
It is carried out by quantitative assessment of similarity and differences in outer to make objective.
No. & codes are assigned to all the characters & the data are then processed using a computer.
It is based on the cytological information like numbers, structure & behavior of chromosomes during cell division specially meiosis.
It is based on chemical constituents (enzymes, hormones, proteins, etc.) of plants.
DIVISION THALLOPHYTA [Algae]
Algae are chlorophyll bearing simple, thalloid, autotrophic and largely aquatic organisms.
Some algae form occurs on moist soil, rocks, tree trunk; some are epiphytes on animals like sloth bear and some are symbionts in lichen.
Vegetative reproduction occurs by fragmentation.
Asexual reproduction occurs during favourable conditions by the formation of zoospores (motile, flagellaed) or aplanospores.
Sexual reproduction may be Isogamous (two morphologically similar gametes) for example – Spirogyra; Anisogamous (structurally dissimilar gametes) For example- Chlamydomonas) or Oogamous (motile small male gamete & non motile bigger female gamete) For example- Volvox)
Embryonic stage is not present.
Classification of Algae:-
Algae are classified on the basis of pigmentations, stored food & flagellation.
The 3 main classes of algae are:-
Chlorophyceae [Green Algae]
Phaeophyceae [Brown algae]
Rhodophyceae [Red Algae]
They have characteristics pigments- chlorophyll a-, b, Xanthophyll & carotens.
They have characteristic pigments – Fucoxanthin, chlorophyll-a, c, xanthophylls & carotens.
They have characteristic pigments – r – phycoerythrin along with chlorophyll –a & d.
The reserve food materials are in the form of pyrenoids (starch + protein), oil droplets.
The reserve food material are in the form of laminarin & mannitol
The reserve food material is in the form of floridean starch. [Amylopectin]
Phycocolloids are absent.
Phycocolloids are absent.
Phycocolloids are present.
2-8, equal apical
They have flagellated gametes & zoo- spores.
They don’t have any flagellated & motile structure.
Ex. – Spirogyra; Volvox, Chara, chlamydomonas.
Ex. – Laminaria and Sargassum, Fucus.
Ex. – Gelidium, Porphyra or polysiphonia.
Economic importance of Algae:-
Algae are responsible for CO2 fixation by the process of photosynthesis.
The algae Gelidium and Gracilaria are used to produce Agar which is used in preparation of ice- cream & jellies.
Some protein rich algae like chlorella & spirulina are used as food supplements by sailors & space – travelers.
Some forms of marine brown algae [Algin] & red algae [carrageenan] produce hydrocolloids which have many commercial uses.
Marine algae are used as food [Ex.- Porphyra, laminaria & sargassum]
DIVISION:- BRYOPHYTES:- (Amphibians of plant kingdom)
It includes various Mosses & Liverworts which are non- vascular embryophytes characterized by presence of independent gametophyte & parasitic saprophytes.
They are called amphibians of the plant kingdom because they can live in soil but are dependent on water for sexual reproduction.
These are attached to the substratum by unicellular or multicellular rhizoids.
The dominant phase of the plant body is the gametophyte; it is haploid and produces gametes for sexual reproduction.
The sex organs are multicellular & have sterile jacket layer.
The diploid zygote represents the first cell of sporophyte that undergoes mitotic division & forms the saprophytic body which is dependent on gametophyte.
The male sex organ in bryophyte is called Anthreidium [produces biflagellate antherozoides] & the flask shaped female sex organ is called archigonium [produces single egg].
The sporophyte at maturity bears sporangia where the spore mother cell undergoes meiosis to form haploid spores, which germinate to produce gametophyte plant body (Protonema)
Bryophytes are broadly divided into:- Liverworts & Mosses.
LIVERWORTS:- (Marchantia, Riccia, etc.)
The plant body (gametophyte) is dorsiventral thallus, closely appressed to the substratum, the leafy members have tiny leaf-like appendages borne on the stem like structure.
Rhizoids are unicellular.
Vegetative reproduction is by fragmentation or by formation of gemmae. (Green multi cellular asexual bud).
Sex organ may be born on the same thallus or on different thalli.
Fertilization occurs inside Archegonium & zygote develops into sporophyte which is differentiated into foot, Seta & capsule & spores are produced within capsule through meiosis which germinate to produce gametophyte.
MOSSES [Funaria & Sphagnum]
The dominant phase is gametophyte which occurs in two stages:-
The protonema stage
The erect leafy gametophyte plant
Rhizoids are multicellular.
Vegetative reproduction is by fragmentation & by budding in the secondary protonema.
Sex organs are produced in clusters at the apex of the leafy shoot. The zygote develops into a sporophyte which is differentiated into, foot, Seta & capsule. And spores are produced in capsules which germinate to produce primary protonema which later produces secondary protonema that form erect leafy plants.
Differences between Liverworts & Mosses:-
The plant body is dorsiventral thallus.
Rhizoids are unicellular & unbranched.
Plants bear scales.
The sporophyte is simple & embedded in the thallus itself. It is the sporogonium where spores are formed.
Spores germinate into gametophytic thallus.
Mid- rib is not present in leaves.
Plant body is leafy gametophyte with radial symmetry.
Rhizoids are multicellular & branched.
Scales are absent.
The sporophyte is differentiating into foot, Seta & capsule and spores are present in the capsule.
Spores germinate into protonema, juvenile gametophytic stage.
Leaves have an unbranched mid- rib.
Some mosses provide food to herbivorous plants.
Sphagnum provides peat which has been used as fuel.
Due to water holding capacity, species of sphagnum are used as packing material for trans – shipment of living materials.
Some mosses are pioneer species to colonise rocks along with lichens & bring about ecological succession.
Mosses form dense mats in the soil & prevent soil erosion.
Marchantia has medicinal properties to cure lungs & liver infection.
These are the first terrestrial plants to possess vascular tissues & called cryptogams.
The dominant phase is sporophyte & it is differentiated into true roots, stems & leaves, all of which possess vascular tissues.
At maturity certain leaves are modified into sporophylls & bears sporangia. Spore mother cells differentiated within sporangia undergo meiosis to produce spores.
All the spores may be of one type (homospores) as in Dryopteris & in other ferns are of two types (heterosporous) i.e., Megospore & microspore as in Selaginella.
The spores germinate to produce gametophyte which is multicellular, free living, thalloid & also called prothallus in ferns.
Fusion of gametes occurs inside the Archegonia & the zygote develops into a sporophytic plant.
Embryo formation takes place.
Classification of Pteridophyte:-
Psilopsida – Ex – Psilotum
Lycopsida – Ex – Lycopodium & Selaginella
Sphenopsida – Ex – Equisetum
Pteropsida – Ex – Dryopteris & Pteris
Pteridophytes are a good source of food for animals. For example Marsilea.
Ferns protect soil from soil erosion.
Equisetum used in scrubbing & polishing.
Azolla (water fern) has a symbiotic association with Anabaena, so it acts as a biofertilizer.
Lycopodium is used in treatment of rheumatism & disorder of lungs & kidney.
Ferns are also grown as ornamental plants.
The gymnosperms are naked seed plants i.e., their ovules are exposed & not enclosed in ovaries.
The sporophytic (dominant phase) plants are shrubs or moderate sized or large trees. Sequoia is the tallest tree species.
They have a tap root system & show symbiotic association with fungi to form mycorrhiza (as in Pinus) or with nitrogen fixing cyanobacteria to form coralloid roots (as in Cycas).
Leaves are large, pinnately compound & needle shaped.
Vascular tissues are well developed.
Gymnosperms are heterosporous and produce microspores in the male cones (microsporangia) & megaspores in the female cones (megasporangia).
The plant may be monoecious (Pinus) or dioecious (Cycas).
Spores are formed after meiosis and microspore develops into male gametophyte (pollen grain) & megaspore develops into female gametophyte within ovule.
The pollen grains are carried by wind & deposited on the ovule. A pollen tube carries the male- gamete towards the archigorium. Fertilization occurs in archegonia & zygote develops into embryo, then slowly ovule transforms into seed.
Seeds of pinus gerardiana (chilgoza) are used as food after roasting.
Gymnosperms provide softwood for construction, plywood & paper – industry.
Sawdust of conifers is used in making plastics & linoleum.
Ephedrine an antibiotic is obtained from ephedra.
Resin is a semi – fluid secreted by special tubes of a number of conifers.
Angiosperms are seed – bearing plants or flowering plants.
The ovules are enclosed in ovaries & hence the seeds are found within fruits.
Vascular tissues are well developed. Xylem has vessels & phloem has sieve tubes & companion cells.
Flower, the reproductive structure may be bisexual (monoecious) or unisexual (dioecious).
Male Sex organs:-
Stamens are the male sex organ of a flower. Each stamen has filament & anther.
Anther contain four microsporangia in which microspore mother cells undergo meiosis to form. 4 – microspores, each of which develops into pollen grains (Male gametophyte).
Female Sex organs:-
Pistil/ Gynoecium/ Carpel is the female sex organ of a flower which has 3 parts:-
Each ovule (mega sporangia) has nucellus covered two – integuments except at the micropile end. Only 1 – megaspore mother cell in the nucellus undergo meiosis to form only 1 – functional megaspore which forms the female gametophyte (embryo sac)
An embryo sac contains egg apparatus consisting of 1- female gamete & 2 – synergids (at micropile end) and 3 – Antipodal cells (at the chalazal end) & two polar nuclei in the central cells which later fuse to form diploid secondary nucleus.
Reproduction :- (fertilization)
PollenGrains are brought to the surface of the stigma of the pistil during pollination.
Each pollen grain germinates forming a pollen tube that carries 2 – male gametes to the embryo sac.
One of the male gamete fuses with the female gamete (egg cell) to form a zygote (syngamy). And the second male gamete fuses with the diploid secondary nucleus to form triploid primary endosperm nucleus (PEN) (Triple fusion).
Since, there are 2 fusion in an ovule during fertilization, this phenomenon is called double fertilization.
After fertilization synergids & anti – podal cells are degenerate. Zygote develops into embryo & PEN develops into endosperm. The ovule gradually transforms into seeds & the ovary becomes the fruit.
Classification of Angiosperms:-
Angiosperms are classified based on the no. of cotyledons in their seeds, into two classes:-
Monocotyledonae:- which have 1 cotyledon
Dicotyledonae:- which have 2 – cotyledons.
They contain 1 cotyledon.
Leaves have 11 venation.
Fibrous root system is present.
Flowers are trimerous.
Stomata are dump- bell shaped.
Cambium is absent.
Secondary growth is absent.
Vascular bundles are scattered.
They contain 2 cotyledons.
Leaves have reticulate venation.
Tap root system is present.
Flowers are pentamerous.
Stomata are kidney shaped.
Cambium is present.
They show secondary growth is stems.
Vascular bundles are arranged in rings.
Angiosperms are major source of food, fibres, spices & beverages.
They also provide valuable timber & medicines.
Alternation of Generation:-
In the life – cycle of sexually reproducing plants, there is a regular alteration between the gamete producing, haploid gametophyte & the spore producing, diploid sporophyte, each producing the other.
Patterns of life cycle:-
Haplontic life cycle:-
The dominant phase in the life cycle is the free living gametophyte.
The diploid phase is represented only by a single celled zygote.
Zygote undergoes meiosis to form ‘haploid spores' which form the gametophyte. For example. most of the algae like volvox, spirogyra etc.
Diplontic life cycle:-
Plants showing this type of life cycles, the dominant photosynthetic phase is the diploid sporophyte .
The haploid phase is represented by a short –lived and one or few celled gametophyte. For example:- All gymnosperms, all angiosperms & algae like focus.
(iii) Haplo Diplontic Life Cycle:-
Both the sporophytic & gametophytic phases are multicellular and dominant phase in the life cycle may be gametophyte or sporophyte.
In Bryophytes, the dominant & the independent phase is thalloid or gametophyte & it alternates with the relatively short lived multicellular sporophyte which is dependent on gametophyte.
In Pteriodphytes, the dominant phase is represented by independent sporophytic plant body. It alternates with the short lived multicellular autotrophic & independent gametophyte. For example- Bryophytes, Pteridophytes & some algae like ectocarpus.
These pteridophytes produce only 1 kind of spores.
Each spore germinate into monoecious prothallus that bears both Antheridia & Archegonia.
These produce 2 types of spores- Micro & Megaspores.
Microspore germinates into male gametophyte & megaspore germinates into female gametophyte.
Ex- Selaginella, Salvinia.
The dominant phase is gametophyte.
Vascular tissues are absent.
Sporophyte is dependent on gametophyte.
True stem & leaves are not present.
Roots are absent, rhizoids are present.
The dominant phase is sporophyte.
Vascular tissues are present.
Sporophyte has independent existence.
It has true stem & leaves.
Roots are present.
Vessels or tracheids are absent in xylem.
Phloem contains sieve cells.
Sporophylls are aggregates to form cones.
Ovules are exposed.
Seeds exposed because there is no ovary, so no fruit formation.
Endosperm is diploid & forms before fertilization.
Trachea is present in xylem.
Phloem contains sieve tube & companion cells.
Sporophylls are aggregated flower.
Ovule are enclosed in ovary.
Seeds are enclosed in fruits which forms after fertilization.