3. Cosmos sulphureus Cav. (sulphur cosmos)

Pl. 276 f; Map 1168

Stems 15–200 cm long, glabrous or sparsely pubescent with short, appressed-ascending and/or longer, spreading hairs, rarely minutely roughened to the touch. Leaves sessile or with a petiole to 70 mm long. Leaf blade 1–15 cm long, 1 or 2 times pinnately lobed, the ultimate segments oblong-triangular to oblong-lanceolate, not threadlike, mostly 2–5 mm wide. Involucre 8–14 mm long, 6–10 mm in diameter, the outer series of bracts 4–8 mm long, spreading to loosely ascending, linear to narrowly triangular or narrowly lanceolate, tapered to a sharply pointed tip, sometimes with slender, white margins; the inner series of bracts 7–12 mm long, erect or strongly ascending, oblong-lanceolate to narrowly oblong-ovate, rounded or more commonly angled to a bluntly or sharply pointed tip, mostly with relatively broad, white margins. Ray florets with the corolla 1.5–3.0 cm long, yellow to orange or reddish orange. Disc florets with the corolla 5–7 mm long, yellow to yellowish orange. Fruits 15–30 mm long (including the beak), the surface minutely pubescent with sparse to moderate, ascending hairs or rarely glabrous. 2n=24, 48. August–October.

Introduced, uncommon and sporadic (native of Mexico, Central America, South America, Caribbean Islands; introduced widely in the eastern U.S. west to Missouri and Texas, also California). Railroads, roadsides, and open, disturbed areas.

Sherff (1955) separated native Latin American populations of this species into three varieties, based on minor differences in pubescence and persistence of the pappus. The introduced Missouri plants appear to represent var. sulphureus (with nearly glabrous stems and mostly persistent pappus) if these taxa are accepted. However, the variability of plants in nature and the effects of plant breeding on the cultivated races has obscured the supposed differences among the varieties, making it imprudent to attempt their formal taxonomic recognition.