The Glumiflorae are among the most ecologically important groups of plants on earth, which is rather surprising, since they have not been around for very long (geologically-speaking!). The dry interiors of most continents are dominated by vast grasslands, and wetlands worldwide are populated by stands of rushes, sedges, and cat-tails.
This widespread distribution is not the only importance of the group, for many animals depend upon graminoids for shelter and food. Many birds depend upon rushes and grasses for their nesting materials and for cover. Prairie and savanna grasses provide both food and cover for a wide variety of rodents, birds, and other small creatures. Many animals, especially ungulates, have undergone much structural evolution as a result of spreading grasslands in the Cenozoic; the best known example being the evolution of the modern horse. The spreading grasslands replaced forest over large areas on several continents, changing the appearance and ecology of the land. The result was a selection for faster-running grazers and small burrowing animals.
The environmental trigger which probably pushed grasslands onto the scene was the drying of the land. In North America, this is attributed to the rise of the Rocky Mountains, which blocked moisture from the Pacific. Associated with this drying came a regime of periodic fires. Plants native to central grasslands have many features which permit them to recover from fire, and many species seem to depend on periodic burning of their competitors to survive.
One feature that has contributed to the success of this group is their ability to spread vegetatively by creeping stems. Unlike trees and most herbs, the Glumiflorae have a primary stem that grows along the surface of the ground, or even underground as in bamboo. This hides the growing apex of the plant from the environment, protecting the sensitive tip from grazing herbivores and frost. A second, and perhaps more important feature of graminoid biology, is their pollination by wind.
Members of the Glumiflorae are anemophilous, or wind-loving. This term refers to the way in which these plants are pollinated. Rather than relying on insects or birds to carry their pollen, graminoids make use of the wind. This is possible because of the habitat in which most species live: open windy regions. Also, they produce large quantities of pollen, to ensure that some will make it to another plant; wind is not as choosy in where it deposits pollen as insects are. This reliance on wind pollination is probably responsible for the loss of petals and sepals in most members of this group.