Cosmos

Annuals [perennials or subshrubs], 30–250 cm. Stems usually 1, erect or ascending, branched distally or ± throughout. Leaves mostly cauline; opposite; petiolate or sessile; blades usually 1–3-pinnately lobed [undivided], ultimate margins usually entire, faces usually glabrous, sometimes glabrate, hispid, puberulent, or scabridulous. Heads radiate, borne singly or in corymbiform arrays. Calyculi of [5–]8 basally connate, ± linear to subulate, herbaceous (striate) bractlets. Involucres hemispheric or subhemispheric [cylindric], 3–15 mm diam. Phyllaries persistent, [5–]8 in ± 2 series, distinct, lanceolate, lance-oblong, lance-ovate, or oblong, ± equal, membranous or herbaceous, margins ± scarious. Receptacles flat, paleate; paleae falling, linear, flat or slightly concave-convex, scarious (entire). Ray florets [0, 5] 8 (more in “double” cultivars), neuter; corollas white to pink or purple, or yellow to red-orange. Disc florets 10–20[–80+], bisexual, fertile; corollas yellow [orange] (at least distally), tubes shorter than funnelform throats, lobes 5, ± deltate (staminal filaments hairy near anthers; style branches linear, flattened, thicker distally, hirtellous, appendages relatively slender). Cypselae (dark brown or black) relatively slender, quadrangular-cylindric or -fusiform [outer somewhat obcompressed], sometimes slightly arcuate, attenuate-beaked, not winged [winged], faces glabrous or hispid to scabridulous or ± setose, sometimes papillate, usually with 1 groove; pappi persistent [falling], of 2–4[–8] retrorsely [antrorsely] barbed awns, sometimes 0. x = 12.

Distribution

Tropical and subtropical America, especially Mexico, widely introduced elsewhere.

Discussion

Species ca. 26 (4 in the flora).

Selected References

Pandey, A. K., S. Chopra, and R. P. Singh. 1986. Development and structure of seeds and fruits in Compositae: Cosmos species. J. Indian Bot. Soc. 65: 362–368.

Sherff, E. E. 1955. Cosmos. In: N. L. Britton et al., eds. 1905+. North American Flora. 47+ vols. New York. Ser. 2, part. 2, pp. 130–146.

Lower Taxa

Cosmos bipinnatus, Cosmos caudatus, Cosmos parviflorus, Cosmos sulphureus

Key

1	Ray laminae yellow to red-orange	Cosmos sulphureus
1	Ray laminae pink, purple, purplish, rose-pink, violet, or white	> 2
2	Leaves: ultimate lobes 2–10 mm wide	Cosmos caudatus
2	Leaves: ultimate lobes to 1.5 mm wide	> 3
3	Ray laminae 15–50 mm	Cosmos bipinnatus
3	Ray laminae 5–9 mm	Cosmos parviflorus