There are nearly half a million species of plants on the earth. With the exception of few , all of them need three basic ingredients to survive : air , light and water . Plants are found in almost every type of habitat. They take their own food using simple raw materials and energy from the sun. Plants requires water to grow. They cannot get this water unless it is available in the soil. Plants obtain water from the soil through their roots. It then passes up the stem to the leaves and flowers. The plant does not take all the water available in the soil. Much of the remaining water evaporates into the surrounding air. The plants can be divided in to the following categories.
Non-Green Plants :
This is a group of plants having simple plant body without root, stem and leaves. They do not contain chlorophyll and hence do not involve photosynthesis. They can grow without the aid of sunlight and seem to popout of the ground overnight. Typical examples of nongreen plants are bacteria , fungi and viruses.
Green Plants :
These are those plants which contain chlorophyll and carry out photosynthesis. There are two categories of green plants : non-flowering and flowering plants.
a. Non-Flowering Plants (Cryptogams).
These are seedless green plants. They reproduce by means of spores. these plants have existed on earth for much longer than flowering plants. Many of them have remained almost unchanged for million of years. They generally have a simple structure and , with the exception of ferns , do not have supporting fiber.
b. Flowering Plants ( Phanerogams ).
These are seed containing green plants . There are two groups of seed plants : the gymnosperms and the angiosperms. This division is based on the type of seeds they have. The gymnosperms are the pine, fir , cedar , cypress and spruce three while the angiosperms include most other trees , the flowering plants, the grasses , crop plants , vegetable and weeds.