Cosmos is a genus of flowering plants in the daisy family (Asteraceae), placed in the order Asterales. The genus comprises around 35 accepted species, all native to the Americas, with the greatest diversity concentrated in Mexico. Plants are herbaceous annuals or perennials, typically growing 0.3 to 2 metres tall. The leaves are simple, pinnate, or bipinnate, arranged in opposite pairs along the stems. Flowers are produced in composite heads (capitula) characteristic of the daisy family, with a ring of broad, showy ray florets surrounding a central cluster of disc florets; flower colour varies considerably across species and includes white, pink, magenta, orange, and yellow. Several species are widely cultivated as ornamental garden plants, and numerous hybrids and named cultivars exist. The genus name Cosmos derives from the Greek κόσμος, meaning either "(ordered) world" — a reference to the neat arrangement of the flower's parts — or from κόσμημα (kósmima), meaning "jewel", evoking the vivid colours of the flower heads. Cosmos species are distributed from the southwestern United States south through Mexico and Central America to northern Argentina, primarily in scrub and meadowland habitats. One species, Cosmos bipinnatus, has naturalized broadly across eastern North America. The genus was also inadvertently introduced to eastern South Africa during the Anglo-Boer War via contaminated horsefeed and is now widespread on the high eastern plains of that region.
Etymology
The generic name Cosmos is derived from the Greek κόσμος (kósmos), which may refer either to "(ordered) world" — alluding to the neat, symmetrical arrangement of the floral structures — or from κόσμημα (kósmima), meaning "jewel", in reference to the jewel-like colours of the composite flower heads.
Distribution
Cosmos species are native to scrub and meadowland in the Americas, ranging from Colorado and Missouri in the United States southward through Mexico — where the greatest species diversity occurs, with 33 of the 35 species — through Central America and into northern Argentina. Cosmos bipinnatus has naturalized widely across the eastern United States and eastern Canada. The genus was introduced to the high eastern plains of South Africa during the Anglo-Boer War via contaminated horsefeed, and it is now widespread there.
Ecology
In their native range, Cosmos species grow in open scrub and meadowland habitats across the Americas, with the highest concentration of species diversity in Mexico. The showy ray florets attract a range of pollinators. Cosmos bipinnatus has proven highly successful outside its native range and has naturalized extensively in eastern North America.
Cultivation
Several Cosmos species are popular ornamental garden plants, valued for their large, brightly coloured daisy-like flowers and ease of cultivation. Numerous hybrids and cultivars have been developed and named, particularly within Cosmos bipinnatus (garden cosmos, in shades of white, pink, and magenta) and Cosmos sulphureus (sulphur cosmos, in yellows and oranges). Plants are generally grown as annuals in temperate gardens.
History
Cosmos was inadvertently introduced to South Africa during the Anglo-Boer War (1899–1902) through contaminated horsefeed imported from the Americas. The plants established themselves on the high eastern plains of South Africa, where they are now a familiar and widespread feature of the late-summer landscape, despite being non-native.
