Plant phylogeny

Plant phylogeny is the historical path from unicellular algae to flowering plants. Cyanobacterial photosynthesis enriched the atmosphere with oxygen, then green and red algae developed in water. When water bodies shrank some algae came onto land, where drying out, obtaining water and minerals, and support became problems; the result was the formation of roots and the leafy stem, and of covering, conducting and mechanical tissues. In the Silurian, about 430 million years ago, rootless and leafless psilophytes (Rhynia, Cooksonia) appeared. In the Devonian clubmosses, horsetails and ferns developed; mosses, however, have no true conducting tissue or roots. In the warm, wet swamps of the Carboniferous forests of tree-like clubmosses (Lepidodendron), horsetails and ferns dominated; their remains did not decay in swampy, oxygen-poor conditions and formed coal; seed ferns were ancestors of gymnosperms. In the Permian the climate dried and many large spore plants died out, and from the Triassic gymnosperms dominated; angiosperms spread rapidly in the Early Cretaceous (about 130 million years ago) and became dominant from the middle of the Cretaceous.