Cosmos, genus of garden plants of the family Asteraceae, containing about 40 species native to tropical America. They have leaves opposite each other on the stem and heads of flowers that are borne along on long flower stalks or together in an open cluster. The disk flowers are red or yellow. The ray flowers, sometimes notched, may be white, pink, red, purple, or other colours. The common garden cosmos, from which most annual ornamental varieties have been developed, is Cosmos bipinnatus.