Annual herb to 2 m tall, glabrous or hairy. Stems erect, unbranched. Leaves to 12 cm long, twice divided into narrow segments. Capitula solitary, to 8 cm across; mostly spring. Ray florets pink, lilac, red or white. Disk florets yellow. Achenes to 16 mm long, beaked, hairy towards apex. Pappus of 2 or 3 barbed bristles or absent.
S USA, Mexico
Available in a wide range of dwarf, variably coloured, single and semi-double cultivars used as border and bedding plants.
C. atrosanguineus (Hook.) Voss, Black Cosmos, from Mexico is a tuberous perennial to 60 cm tall with once or twice divided leaves, solitary capitula to 4.5 cm across and dark red florets.
C. diversifolius Otto. from C America is a tuberous perennial to 90 cm tall with simple to divided leaves, solitary capitula to 7 cm across, pink or lilac ray florets and yellow disk florets.
C. sulphureus Cav., Yellow Cosmos, from N, S and C America is an erect annual to 2 m tall with once or twice divided leaves, solitary capitula to 7 cm across and yellowish florets.
Source: (2002). Asteraceae. In: . Horticultural Flora of South-eastern Australia. Volume 4. Flowering plants. Dicotyledons. Part 3. The identification of garden and cultivated plants. University of New South Wales Press.