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

Hymenoxys cooperi (A. Gray) Cockerell, Bull. Torrey Club
31: 394. 1904.
Actinella Cooperi A. Gray, Proc. Am. Acad. 7: 359. 1868. Picradenia Cooperi Greene, Pittonia 3: 272. 1898.
Hymenoxys Cooperi Grayi Cockerell, Bull. Torrey Club 31: 495. 1904. Hymenoxys Cooperi argyrea Cockerell, Bull. Torrey Club 31: 495. 1904.
A perennial, with a tap-root and a somewhat cespitose crown; stems 5-10 dm. high, with slender branches, finely puberulent or glabrate; leaves 4-10 cm. long, divided into 3-5 linearfiliform divisions, glabrate and strongly punctate; heads in an open corymb; peduncles 3-10 cm. long; involucre somewhat turbinate, 5 mm. high, about 8-12 mm. broad; outer bracts about 8, keeled, glabrate, united about one third their length, the free portions lanceolate; inner bracts elliptic, acute, erose on the margins; ligules 8-10 mm. long, 3 mm. wide; disk-corollas
3 mm. long, densely glandular-puberulent; achenes 3 mm. long, densely hirsute; squamellae 1-1.5 mm. long, obtuse or acute at the apex.
Type locality: Providence Mountains, in the Mojave district, California. Distribution: Southern California and Arizona.

Hymenoxys canescens (D.C. Eaton) Cockcrcil, Bull. Torrey
Club 31: 484. 1904.
Actinclla Richardsoni canescens D.C. Eaton, in S. Wats. Bot. King's Expl. 175. 1871. Picradenia canescens Greene, Pittonia 3: 271. 1898.
A perennial, with a somewhat branched caudex; stem 1-2 dm. high, canescent with flat scale-like hairs; leaves numerous, 2-4 cm. long, divided into 3-5 linear-filiform divisions, canescent like the stem, rather fleshy; heads 1-3; peduncles 1-3 cm. long; involucre depressedhemispheric, 5-6 mm. high, 10-15 mm. broad; outer bracts 12-15, lanceolate, canescent, united only at the base; inner bracts ovate-lanceolate, acute, barely erose; ligules about 8 mm. long, 3 mm. wide; disk-corollas 4 mm. long, densely glandular; tube 1 mm. long; achcnes 3 mm, long, densely hirsute; squamellae 2 mm. long, ovate, acute.
Type locality: East Humboldt Mountains, Nevada. Distribution: Nevada and Utah.

Hymenoxys cooperi is a species of flowering plant in the daisy family known by the common name Cooper's rubberweed. It is native to the southwestern United States and Great Basin, where it grows in rocky soils in arid regions from southern California to New Mexico, north as far as Idaho and Oregon.

Hymenoxys cooperi is a biennial or perennial herb with a branching stem growing erect to heights between 15 and 90 centimeters (6-36 inches or 0.5-3.0 feet). It produces narrow, pointed leaves with two lateral lobes that form a trident shape. The foliage and stem are glandular and waxy, usually with a thin coat of light-colored hairs. The daisy-like flower head is a cup of fused phyllaries with 30–150 tiny yellow-orange disc florets surrounded by 9–14 bright yellow ray florets, each ray about a centimeter (0.4 inches) long.