There are shorter grasses for drier places, huge grasses like pampas grass, decorative grasses, alpine grasses, and so on. All of them have descended from a common ancestor. Grasses have been successful because they have found niches, which are places where there are available resources. There is lots of light where there are no trees between a plant and the sun, so the dry areas offered a niche to plants that did not need so much water. Grasses have developed strategies for dealing with these drier habitats.
Grasses grow rapidly when moisture is available.
The grasses grow quickly, and make seeds. Their dense stands allow for efficient wind pollination. When the hot summers come, the grass stems and blades die. Our hills turn golden brown. The grass remains dormant until the rains return.