The changing water conditions in the terrestrial environments formed the anatomy, the reproduction and the metabolism of the land plants since the beginning of their history. While mosses, some club moss and fern can tolerate transitional dry episodes, the homoiohydric gymnosperms dominated the arid landscapes almost 180–200 million years. Seed ferns, ancient pines, cycads and other gymnosperm groups were the main foods of herbivore therapsids dinosaurs in the great drier areas of the Pangaea. Many of them died out, but the Mormon Tea (Ephedra), the Welwitschia and Cycadaceae species survived the raise of the angiosperms, which originally diverged in the wet tropical territories. The predisposition of angiosperms to become herbaceous created the potential to become into leaf or stem succulents. The C4 based CAM metabolism spread among the succulent plants independently. The coevolution of succulents created deceptively similar species in different plant clades.
