Classification of the Plant Kingdom (Plantae)


>Reproduction is mainly sexual through complex reproductive systems. They are found attached to rocks or other algae. Their reddish colour is due to a pigment called phycaerythrin.

Phaeophyta (Brown algae) – Are multicellular marine plants growing on rocks or attached to sea shores, ranging from a few millimetre to massive plants upto 200ft. Reproduction in these plants is both sexual and asexual. Their brownish colour is due to xanthophyll pigment called fucoxanthin.

Chlorophyta (Green algae) – Are a group of bright green (some 3700 species) mostly aquatic plant, unicellular, colonial and multicellular. Reproduction in these plants is both sexual and asexual. They are found in abundance in fresh water as well as sea water, on tree trunks, moist rocks, leaf surfaces and soil.

Bryophyta – Are simple, non-vascular small plants that grow in moist places. The plant body is thallus-like and remains attached to the soil by rhizoids. They lack roots, flowers and seeds. Reproduction is mainly through vegetative means or sexual, e.g. liverworts, hornworts, mosses, etc.

Lycopodophyta (Club mosses) – Are multicellular terrestrial plants with vascular tissues. Their body is differentiated into root, stem and leaves. Stem not jointed; spores are produced in the axils of fertile leaves, mostly aggregated into club-like terminal cones.

Arthophyta (Horsetails) – Are multicellular plants with vascular tissues. The plant body is divided into root, stem and small whorled leaves. They have upright stems which grow from underground branches. Arthophyta are largely an extinct group represented by a single living genus, the Equisetum (the horsetails).

Pterophyta (Ferns) – Are multicellular plants with vascular tissues; the body is differentiated into root, stem and leaves; contain spores for reproduction which are produced usually in the lower surface of the leaves or on their margins. Seeds are not produced.

Cycadophyta – Are multicellular terrestrial plants with vascular tissues (without vessels). The plant body is divided into root, stem and leaves. The stem is large and woody, leaves are large and fern-like, e.g. Cycas (sago palm), Zamia (sago tree), etc.

Coniferophyta (Conifers) – Are multicellular plants with well developed tissues. The main plant body is large and woody; leaves are simple, smaller than Cycadophyta and needle-like. Examples: Cedrus (deodar), Taxus (yew).

Anthrophyta (Angiosperms) – Are more advanced flowering plants with well-developed vascular tissues, predominantly saprophytic, and a well-differentiated body of roots, stem and leaves. They occur in almost all places and make up more than half of all known species of plants-about 200,000 species. They range in size from minute-floating duckweeds to saint eucalyptus and silk-cotton trees, and include plants of a great variety of forms – cacti, water lilies, sunflowers, orchids, pitcher plants, Indian pipe, etc. The reproductory organ of these plants are flowers, and the seeds are enclosed within an ovary which develops into a fruit-wall. The distinct parts of the body of these plants are:

Root – is the descending and positively geotropic part of the plant, which develops from the radical or the primary root. It anchors the plant to the soil and absorbs water and minerals and salts from the soil.

Stem – is the ascending and negatively geotropic part of the plant. It bears nodes and internodes and support leaves, flowers and fruits.

Leaves – are generally green and carry out the function of synthesis of food (photosynthesis).

Flower – is the reproductive organ of angiosperms. It generally consists of four whorls: sepals, petals, stamens and pistils. After pollination and fertilisation the ovary of the pistil develops into fruits and the ovules into seeds. Some flowers are found in groups or clusters which are called peduncle. The arrangement of flowers on the peduncle is called inflorescence. The ripened ovary becomes a fruit which generally contains seeds. On the basis of morphology, Angiosperms are further classified into: (i) herbs, (ii) shrubs and trees.

On the basis of age, they are grouped as:

(i) Perennials – which live for many years.
(ii) Annuals – which produce flowers and fruit in the course of a single season.
(iii) Biennials – which live for two seasons.

There are two major classes of Angiosperms, viz:

(1)Dicotyledons – These plants have two cotyledons in their seeds and may be annuals, biennials or perennials, e.g. gram.
(2)Monocotyledons – These are mostly annuals and have only one cotyledon in their seeds.

Other Classifications
1.Terrestrial – Plants which grow on soil.
2.Hydrophytes – Plants which grow in water.
3.Epiphytes – Plants which perch on other plants but do not take nourishment from them. They are not rooted in soil but grow upon branches and stems of other plants, e.g. urn plant.
4.Xerophytes – are adapted to grow in a dry habitat like desert and can survive without moisture, e.g. Cacti.
5.Mesophytes – thrive under conditions intermediate between very wet and very dry. The great variety of crops, e.g. beans, tomatoes, peas, etc. belong to this category.
6.Parasitic – which depend on other plants for their nourishment. They lack chlorophyll and thus cannot make their own food, e.g. bacteria and fungi.
7.Carnivorous – Plants which traps insects and other small creatures on their sticky leaves and digest them to obtain nitrogen and other material essential for their growth. They are also called insectivorous plants. E.g. pitcher plant and bladderwort.

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