views updated

Trifolium (clovers; family Leguminosae) A genus of annual or perennial herbs, with leaves that are trifoliate, stalked, and with stipules adnate to their stalks. The flowers are usually in dense, racemose heads, with short stalks or none. The petals are persistent, and the pods very small, short, and indehiscent, remaining enclosed in the calyx, and often also by the standard petal. The genus includes many important fodder plants (especially T. pratense and T. repens) and, like other Leguminosae, fixes nitrogen by means of root-nodule bacteria, so increasing soil fertility. There are 238 species, centred in southern Europe and western Asia but extending to other temperate and tropical regions.