Ecological Importance

The most recent classification of the grass family recognizes twelve subfamilies:

With 10,025 known species, the Poaceae is the fourth largest plant family. Only Orchidaceae, Asteraceae, and Fabaceae have more species, although with over 10,000 species the Rubiaceae is not far behind.

Biomes dominated by grasses are called grasslands. If only large contiguous chunks of grasslands are counted, these biomes cover 31% of the planet's land. Grasslands go by various names depending on location, including pampas, plains, steppes, or prairie.

In addition to their use as forage worldwide by many grazing mammals such as cattle and other livestock, deer, and elephants, grasses are used as food plants by many species of butterflies and moths; see List of Lepidoptera that feed on grasses.

The evolution of large grazing animals in the Cenozoic has contributed to the spread of grasses. Without large grazers, a clearcut of fire-destroyed area would soon be colonized by grasses and, if there is enough rain, tree seedlings. The tree seedlings would eventually produce shade, which kills most grasses. Large animals, however, trample the seedlings, killing the trees. Grasses persist because their lack of woody stems helps them to resist the damage of trampling.