burhead (genus Echinodorus), genus of some 28 species of annual or perennial herbs of the family Alismataceae, named for their round, bristly fruit. The aquatic plants grow in shallow ponds and swamps in North and South America. They are slender plants that are seldom more than 30 cm (12 inches) tall. They can live completely submerged under water and have rhizomes and adventitious shoots that facilitate asexual reproduction. Their leaves are spear-shaped or oval-shaped and can be sessile (leaf blade attached directly to the stem) or grow on long basally clustered petioles (stalks that connect leaf blades to the stem). The characteristic flowers have three white or pink petals and three green sepals and are often arranged in whorls of three to six along the stem. The fruit is a spherical aggregate of achenes.
E. cordifolius, which has a creeping stem and large ovate leaves, occurs in southern North America. E. tenellus has spear-shaped leaves about 5 cm (2 inches) long and occurs throughout eastern and southwestern North America, the West Indies, and South America. A number of species are cultivated as aquarium plants and are commonly sold as “sword plants.”