It is not known exactly how many plant species exist on the earth today, but the number is estimated at more than half a million. Botanists have described and named some 325,000 species so far, including 26,000 different kinds of mosses, which have very simple structures, and around 250,000 flowering plants, whose roots, stems, leaves and flowers are extremely complex.
The cover of vegetation protects rocks and the ground from weathering. Trees, shrubs and grasses, depending on their density, absorb a large proportion of the rainfall. Their roots hold the ground together. For this reason, the water and wind are nearly unable to attack the ground.
