Cooper's Rubberweed

Some plants of Hymenoxys cooperi, mostly 10–40 cm with mostly 1–6 heads, have been called var. canescens.

Biennials or perennials, (10–)20–80(–100) cm (monocarpic; sometimes with sparingly branched, woody caudices). Stems 1–3(–15), usually purple-red-tinted proximally, sometimes purple-red-tinted throughout, branched distally, ± hairy. Leaves: blades simple or lobed (lobes 3–9), ± hairy, gland-dotted (basal leaf bases ± long-villous-woolly); mid leaves lobed (lobes 3–5, terminal lobes 1–2.5 mm wide). Heads (1–)7–45(–80) per plant, in paniculiform to corymbiform arrays. Peduncles (2–)3.5–8(–13) cm, ± hairy. Involucres subhemispheric to hemispheric, 8–10 × 10–17 mm. Phyllaries in 2 series, unequal; outer 8–15, basally connate ¹/3–¹/2 their lengths (moderately to strongly keeled), lanceolate, 4.5–8.9 mm, apices acuminate to acute; inner 14–22, obovate to oblanceolate, 4.1–6.8 mm, apices acuminate to mucronate. Ray florets 9–14; corollas yellow, 10.2–17(–21.5) × 4–7.5(–9.2) mm. Disc florets 30–150+; corollas 2.7–4.8 mm. Cypselae narrowly obpyramidal, 1.7–3.7 mm; pappi of 5–6(–8) obovate, aristate scales 1.3–3.3 mm. 2n = 30.

Actinella cooperi A. Gray, Proc. Amer. Acad. Arts 7: 359. 1868; Hymenoxys cooperi var. canescens (D. C. Eaton) K. F. Parker