10. Mentzelia argillosa J. Darlington, Ann. Missouri Bot. Gard. 21: 153. 1934.
[C E F]
Arapien blazingstar Arapien blazingstar
Nuttallia argillosa (J. Darlington) W. A. Weber
Plants perennial, bushlike, with subterranean caudices. Stems multiple, erect, zigzag or straight; branches distal or along entire stem, distal longest or all ± equal, antrorse, straight; hairy. Leaves: blade 15.4–40(–86) × 4–12.2 mm, always some more than 10 mm wide, widest intersinus distance 4–12.2 mm; proximal oblanceolate to spatulate, margins usually entire, rarely dentate, teeth 0(–4), perpendicular to leaf axis, 0.1–1 mm; distal oblanceolate, spatulate, or elliptic, base not clasping, margins usually entire, rarely dentate, teeth 0(–4), perpendicular to leaf axis, 0.3–1.4 mm; abaxial surface with simple grappling-hook, complex grappling-hook, and needlelike trichomes, adaxial surface with simple grappling-hook and needlelike trichomes. Bracts: margins entire. Flowers: petals golden yellow, 8.2–12.2(–15.2) × 2.4–5 mm, apex acute, glabrous abaxially; stamens golden yellow, 5 outermost petaloid, filaments narrowly spatulate, slightly clawed, 5.6–11(–13.5) × 1.4–3 mm, with anthers, second whorl with anthers; anthers usually twisted after dehiscence, epidermis papillate; styles 5.5–9.4 mm. Capsules cup-shaped, 5–8.4 × 3.1–6 mm, base tapering to rounded, not longitudinally ridged. Seeds: coat anticlinal cell walls straight, papillae 3–5 per cell. 2n = 22.
Flowering Jun–Aug. Sparsely vegetated steep cliffs or slopes composed of gypsum-rich clayey and gravelly soils; of conservation concern; 1600–1900 m; Utah.
Mentzelia argillosa is endemic to the Arapien Shale formation in Sevier and Sanpete counties.