5 Classification of plants

CLASSIFICATION OF PLANTS 
1. Thallophyta. Plant body a thallus, with no distinction of stem, root and leaf. Individuals mostly small with simple organization, many micro­scopic.

• (a) ALGAE. Organisms possessing chlorophyll and sometimes additional pigments. 

1. Euglenophyceae.      Motile protoplasts with no cellulose wall. No sexual reproduction. 
2. Chlorophyceae.      Cellulose wall present. Chlorophyll only. Fresh-water and marine. 
3. Cyanophyceae. Blue-green colour due to phycocyanin. Fresh-water and marine. 
4. Phaeophyceae. Brown colour due to fucoxanthin. Exclusively marine. 
5. Bacillariophyceae. Unicellular forms with silicified cell walls. Brown colour due to diatomin. Fresh-water and manne. 
6. Rhodophyceae. Red colour due to phycoerythrin. Pre­dominantly marine. 

• (b) FUNGI. Organisms devoid of chlorophyll; either saprophytic or parasitic. 

1. Archimycetes.   Thallus a naked mass of protoplasm. Asexual reproduction by spores formed in sporangia. Sexual reproduction by motile gametes. 
2. Phycomycetes.  Thallus a mycelium of non-septate hyphae. Asexual reproduction by spores formed in sporangia, or by conidiospores. Sexual reproduction by variously formed gametes. 
3. Ascomycetes.    Mycelium of septate hyphae. Asexual repro­duction by conidiospores. Sexual reproduction resulting in ascospores formed in sac-like cells (asci) which form a fruiting body. 
4. Basidiomycetes. Mycelium of septate hyphce. Asexual reproduction occasionally by conidiospores. Sexual reproduction resulting in basidiospores borne on short stalks from special cells (basidia) developed on a fruiting body. 

(c) BACTERIA. Minute unicellular organisms, usually devoid of chloro­phyll and without a fully organized nucleus. Reproduction by binary fission and by spores. Sexual reproduction doubtful.
(d) LICHENES. Compound organisms consisting of fungal and algal partners. Reproduction fungal (mostly Ascomycetes).
2. Charophyta. Thallus jointed, branched, attached at the base; con­isting of large coenocytes, containing chlorophyll. Sexual reproduction by antherozoids in antheridia and oospheres in oogonia. Fresh-water.

• (a) CHARALES. The sole order. Characters as above. 

3. Bryophyta. Terrestrial or fresh-water. Gametophyte either a thallus or differentiated into stem and leaves, attached by rhizoids but without true roots. Sexual reproduction by antherozoids in antheridia and oospheres in archegonia. Sporophyte permanently attached to the gametophyte. Homoporous.

• HEPATICAE. Gametophyte thalloid or with leafy stem. Sex organs apical or dorsal. Sporophyte usually non-chlorophyllous. 
• MUSCI. Gametophyte 'with leafy stem. Sex organs apical or lateral. Sporophyte usually chlorophyllous. 

4. Pteridophyta. Mainly terrestrial. Sporophyte with stem, roots and leaves. Vascular tissue present. Spores produced in sporangia. Gameto­phyte a small prothallus bearing antheridia and archegonia.

• (a) PSILOPSIDA.  Sporophyte with small leaves (microphyllous) or none. Homosporous. No true roots. Sporangia free or united into synangia, terminal or on specialized branches. Gametophyte in living forms reduced, saprophytic. 
• (b) LYCOPSIDA. Sporophyte with numerous, usually small leaves (microphyllous). Homosporous or heterosporous. Sporangia free, borne on or axillary to sporophylls. Gametophyte reduced, saprophytic or enclosed in the spores. 
• (c) SPHENOPSIDA. Sporophyte with jointed stems and small leaves In whorls (microphyllous). Homosporous. Sporangia clustered, in terminal strobili. Gametophyte green. 
• (d) PTEROPSIDA. Sporophyte with large leaves (megap~lous). Homo­sporous or heterosporous. Sporangia clustered on foliar organs. Gametophyte either green, or reduced and enclosed in the spores. 

5. Spermatophyta. Sporophyte with stems, roots and leaves. Vascular tissue present. Heterosporous. Microspores (pollen grains) and mega­sporse (embryo sacs) produced in distinctive sporangia. Megasporangia with integuments, developing into seeds. Gametophytes extremely reduced, enclosed in the spores.

• (a) PTERIDOSPERMAE. Leaves fern-like. Sporangia borne on normal or only slightly reduced leaves, not aggregated into flowers. 
• (b) GYMNOSPERMAE. Sporangia aggregated into strobili (cones), each usually containing only one type of spore. Megasporangia exposed.
•  (c) ANGIOSPERMAE. Sporangia either in separate or in the same flowers. Megasporangia enclosed in carpels, which ripen into fruits. 

1. Dicotyledons. Embryo with two cotyledons. Leaves mostly net-veined. 
2. Monocotyledons. Embryo with one cotyledon. Leaves mostly parallel-veined. 

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