Cosmos, a flowering plant native to Mexico and widely cultivated in the United States as a garden flower. The name is applied to about 20 species of annual and perennial herbs of the composite family. They are related to the sunflower and dahlia. Widely grown in the United States are the common cosmos with white, pink, purple, or red petals and yellow disks; and the yellow cosmos, with yellow or orange petals and yellow disks. These plants are annuals, but in warmer climates many cosmos are perennials. The black cosmos is often called a dahlia.

The cosmos has a tall stem. The common cosmos grows from three to four feet (90 to 120 cm) tall; the yellow cosmos, as high as 10 feet (3 m). The large, showy flower heads occur singly or in clusters. The cosmos is an autumn or late-blooming plant that grows best in sandy soil that is not too rich. It is easily grown from seeds started in hotbeds or indoors.

The common cosmos is Cosmos bipinnatus; the yellow cosmos, C. sulphureus; the black cosmos, C. atrosanguineus. All belong to the family Compositae.