1. Plectocephalus americanus (Nuttall) D. Don in R. Sweet, Brit. Fl. Gard., ser. 2. 1: plate 51. 1830.
American basketflower, powderpuff or thornless thistle, American star-thistle, cardo del valle
Centaurea americana Nuttall, J. Acad. Nat. Sci. Philadelphia 2: 117. 1821
Plants 50–200 cm. Stems usually 1, erect, sparingly branched, glabrous, minutely scabrous and glandular. Leaves scabrous; basal sessile or winged-petiolate, usually absent at anthesis, blades oblanceolate to narrowly obovate, 10–20 cm, margins entire or sparingly denticulate; cauline sessile, usually not much smaller except among heads, blades ovate to lanceolate, mostly 5–10 cm, entire or serrulate. Involucres broadly hemispheric, 30–50 mm. Phyllaries: bodies pale green, broadly elliptic (outer) to linear (inner), apices with appendages erect to spreading, whitish to stramineous (less commonly pale brown to purple), fringed with 9–15 slender spinelike teeth 2–3 mm, teeth not conspicuously ciliate. mid with (4–)5–7(–8) pairs of lobes; faces glabrous or loosely cobwebby-tomentose. Corollas of neutral florets pink-purple (rarely white), 35–50 mm, enlarged, raylike; of bisexual florets pinkish, 20–25 mm. Cypselae grayish brown to black, 4–5 mm, glabrous or with white hairs near bases; pappus bristles unequal, stiff, 6–14 mm. 2n = 26.
Flowering Feb–Aug. Prairies, fields, open woods, grasslands, roadsides, other disturbed sites; 0–2100 m; Ariz., Ark., Kans., La., Mo., Okla., Tex.; Mexico (Chihuahua, Coahuila, Nuevo León, San Luis Potosí, Tamaulipas).
Plectocephalus americanus is an attractive and showy plant and has been in cultivation for many years. It occasionally escapes from cultivation outside its native range.