Grass is a type of plant with narrow leaves growing from the base. Their appearance as a common plant was in the mid-Cretaceous period. There are 12,000 species now.[1] A common kind of grass is used to cover the ground in places such as lawns and parks. Grass is usually the color green. That is because they are wind-pollinated rather than insect-pollinated, so they do not have to attract insects. Green is the best colour for photosynthesis.