An Introduction to the Kingdom Plantae

The kingdom plantae or plant kingdom comprises hundreds of thousands of different species. They live in every type of habitat, from frozen Arctic tundra to tropical rain forests and deserts. Plants are multicellular eukaryotes with well-developed tissues. These range in size from minute, almost microscopic duckweed, to massive giant sequoias, some of the largest organisms that have ever lived. One of the unifying characteristics of almost all plants is their mode of autotrophic nutrition.

In the beginning the plants were restricted only to aquatic conditions. The migration started towards land nearly 400 million years ago. Plants are thought to have descended from a common protistan ancestor, an ancient freshwater alga. Because of their common ancestry the living green alga and plants share a number of features. Both contain the same photosynthetic pigments: chlorophylls a and b, carotenes and xanthophylls. Both store carbohydrates as starch, have cellulose in cell wall, in certain details of cell division, including the formation of cell plate during cytokinesis.

Four major groups of plants are living today. These are

(a) Bryophytes

(b) Seedless vascular plants

(c) Gymnosperms

(d) Flowering plants.

Bryophytes are small plants that lack vascular tissues and reproduce spores. The other three groups of plants have vascular tissues xylem and phloem. Seedless vascular plants reproduce by spores like bryophytes.

Gymnosperms are vascular plants and reproduce by forming seeds, borne exposed on a stem or cone. Flowering plants are vascular plants which reproduce by forming seeds enclosed within a fruit. There are about 36000 known species of plants.

Classification

An outline of classification of plant kingdom is given in the following table.

 

i. Division – Bryophyta

Nonvascular plants with a dominant gametophyte generation

(1) Phylum Heptophyta (liverworts).

(2) Phylum Bryophyta (mosses).

(3) Phylum Anthocerotophyta (hornworts).

 

ii. Division Tracheophyta

Vascular plants with a dominant sporophyte generation

 

A. Seedless vascular plants

Phylum Psilotophyta (Psilopida) (whisk ferns)

Phylum Lycopodophyta (club mosses)

Phylum Sphenophyta (Equisetophyta) (horse tails)

Phylum Pterophyta (Pteridophyta) (ferns)

 

B. Seed vascular plants

1. Plants with naked seeds (Gymnosperms)

Phylum Coniferophyta (Pinophyta) (conifers)

Phylum Cycadophyta (cycads)

Phylum Ginkgophyta (maidenhair tree)

Phylum Gnetophyta (Gnetophytes)

 

2. Seeds enclosed within a fruit

Phylum Anthophyta (Magnoliophyta) (angiosperms or flowering plants)

Class Magnoliopsida: Dicotyledons (dicots)

Class Liliopsida Monocotyledons (monocots)