The second largest kingdom of living things after animals is the plants. The key feature of a plant which sets it apart from other living things is that it obtains energy from light by the process of photosynthesis. Most plants have broad, flat surfaces, such as leaves or fronds, where this happens. Just as there are many groups of animals, from simple worms to complicated mammals, so there are many groups of plants. However they are divided into two main kinds—the simpler types without flowers, and those with flowers.
NON-FLOWERING PLANTS
The simplest non-flowering plants are algae. They nearly all live in water, although a few kinds can survive in damp places, like Pleurococcus alga which grows as a green powder on shady tree trunks. Nearly all seaweeds and some types of pondweeds, such as the green, hair-like spirogyra, are algae. An alga has no proper roots, stem or leaves, although it may have a stem-like part and leaf-like blade. It absorbs water and nutrients through its body surface.
Mosses and liverworts are known as bryophytes. A moss has small green leaflets but no proper stem or roots. It absorbs water and nutrients through its leaflets so it can only live in damp places. Liverworts grow in similar places. Each has a low, flattened body known as a thallus.
Ferns, or pteridophytes, are also non-flowering. A fern has roots which absorb water and minerals from the soil, and a stiff stern to hold up its much-branched fronds. The stem, like the stem of a flowering plant, contains tiny pipes or tube-like vessels to carry the water and other substances from the roots to the fronds. Plants with these vessels are known as vascular plants.
All of these non-flowering plants reproduce by making tiny, dust-like spores which grow into new plants. Conifers, also called gymnosperms, reproduce by seeds. The seeds form in hard, scaly structures known as cones. Pines, firs, spruces, larches, redwoods and cypresses are all conifers.
FLOWERING PLANTS
The flowers of flowering plants, also known as angiosperms, are body parts specialized for breeding. The flowers produce seeds which in suitable conditions grow into new plants. Flowering plants are by far the main or dominant group of plants around the world, except for seaweeds in the oceans and the conifer forests in colder regions. Flowering plants include familiar herbs, grasses, reeds, rushes, wild and garden flowers, and most trees and bushes (except for the conifers). There are some 260,000 different kinds or species of flowering plants compared to about 550 species of conifers, 11,000 ferns, 23,000 mosses and liverworts, and around 12,000 species of algae.
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