genus of annual and perennial grasses of the family Poaceae, containing about 400 species distributed throughout warm regions of the world. Some are valuable forage grasses. P. dilatatum, a South American species, is also grown in Australian and North American (where it is known as dallis grass) pastures. Paspalum urvillei, known as vasey grass in North America, is grown as hay in other areas in which it is native. Water couch, or knotgrass (P. distichum), forms large, flat mats along shores and in ditches in North and South America and Europe; it is used as a lawn grass in Australia.