A low-growing annual or perennial, occurring in both temperate and subtropical regions, but mainly in the N hemisphere; leaves with three toothed leaflets; small pea-flowers, white, pink, or red, clustered into often dense, rounded heads; pods small, remaining enclosed by the calyx. The flowers are visited by hive bees, providing an important source of nectar for bee-keepers. Several species are extensively grown as fodder for cattle, and they are also valuable pasture plants, often grown with grasses, enriching the soil through the presence of nitrogen-fixing bacteria in small nodules on the root system. Yellow-flowered species are generally called trefoils. (Genus: Trifolium, 250 species. Family: Leguminosae.)