Today, on Earth there are more than 400000 species of flora. All of them came only from several ancient plants. Some types disappeared from the face of the earth as could not adapt to the changing conditions or did not sustain the competition from another, again appeared plant species.
The most ancient of the known plants are the simplest blue-green seaweed. They represented the unicells functioning by means of one cage deprived of a kernel. Occurred among blue-green seaweed both monocelled, and the metaphytes capable to photosynthesis implementation. Process of photosynthesis promoted receipt in the atmosphere of Earth of oxygen.
About 2600, in a Proterozoic era, Earth was filled by red and green seaweed. In the late Paleozoic (Silurian Period) there are most ancient higher plants, the called riniofita or psilofita. They had escapes, but there were no leaves and roots. Riniofita bred disputes. They grew on the land or partially in water.
Emergence of the higher sporous plants
About 400-360 million years ago there are first pteridophytes and mokhovidny plants relating to the higher sporous plants. On the land the process of division of plants into a root, a stalk and a leaf begins, there are basic fabrics and the vascular carrying-out system.
The first land plants had the small sizes. Gradually there were larger forms of plants – the pteridophytes having roots with root hairs. In the Palaeozoic Era the pteridophytes were the huge plants which filled the land. But because water was necessary for their reproduction, they grew only in the areas having the increased humidity.
Gymnospermous and angiospermous plants
360-280 million years ago (Carboniferous Period) there were seed ferns which became the ancestors of all gymnospermous plants. The huge treelike pteridophytes dominating at that time gradually die off and form coal deposits. In the Permian Period of the Paleozoic the most ancient gymnospermous plants appear. Endangered treelike pteridophytes are succeeded by seed and grassy ferns. About 240 million years ago there came the Mesozoic Era. In its Triassic Period arose modern gymnospermous, and in Jurassic – the first angiospermous plants. They have a flower in which there is a pollination, fertilization and formation of a fruit. It is necessary to carry grassy plants, trees and bushes to Angiospermae. About 70 million years ago the Cenozoic Era begins, the planet is filled by the angiospermous and gymnospermous plants existing to this day. Evolution of plants – very difficult and long process as a result of which on Earth there was all modern variety of plants, including seaweed, ferns, Bryophyta and flowering plants.