Bountiful forests grow in warm and rainy areas. Angiosperms adjust themselves to the harsh environment where forests would not grow. As a result, the tree size has become smaller like grass, and perennial plants have changed to yearly plants and in this way they spread out of forests.
Gramineousplants, which cover the largest areas of the earth's surface, spread in this way. After having been sun-drenched on grassland, they have supported mammalian prosperity and allowed the birthof human civilization.