Plants evolved more than 430 million years ago from multicellular green algae. By 300 million years ago, trees had evolved and formed forests, within which the diversification of vertebrates, insects, and fungi occurred. Roughly 266,000 species of plants are now living. The two major groups of plants are the bryophytes and the vascular plants; the latter group consists of nine divisions that have living members. Bryophytes and ferns require free water so that sperm can swim between the male and female sex organs; most other plants do not. ....