2. Mentzelia humilis (Urban & Gilg) J. Darlington, Ann. Missouri Bot. Gard. 21: 155. 1934.
Mentzelia pumila Torrey & A. Gray var. humilis Urban & Gilg, Nova Acta Acad. Caes. Leop.-Carol. German. Nat. Cur. 76: 93. 1900; Nuttallia humilis (Urban & Gilg) Rydberg; Touterea humilis (Urban & Gilg) Rydberg
Plants perennial, bushlike, with ground-level caudices. Stems solitary or multiple, erect, straight; branches distal or along entire stem, distal longest or all ± equal, antrorse; straight to upcurved; hairy. Leaves: blade 25–95 × 5.5–28(–36.2) mm, widest intersinus distance 0.8–9.1 mm; proximal spatulate to oblanceolate or elliptic, margins pinnate to pinnatisect, lobes 4–16(–20), slightly antrorse or perpendicular to leaf axis, 2.3–11.8(–16.4) mm; distal elliptic, lanceolate, spatulate, or linear, base not clasping, margins entire or dentate to pinnatisect, teeth or lobes (0–)4–16, slightly antrorse or perpendicular to leaf axis, 2.3–13.8(–16.9) mm; abaxial surface with simple grappling-hook, needlelike, and sometimes complex grappling-hook trichomes, adaxial surface with simple grappling-hook and needlelike trichomes. Bracts: margins usually entire, rarely pinnate. Flowers: petals white, 10.3–13(–28.6) × 1.4–4 mm, apex acute, glabrous abaxially; stamens white, 5 outermost petaloid, filaments linear to narrowly spatulate, slightly clawed, 8.8–19(–22.3) × 0.7–3.3 mm, without anthers, second whorl without anthers; anthers straight after dehiscence, epidermis papillate; styles 6.5–11.3 mm. Capsules cup-shaped, 5.3–10.2 × (4.2–)5.2–8.6 mm, base rounded, not longitudinally ridged. Seeds: coat anticlinal cell walls wavy, papillae 6–12 per cell.
Varieties 2 (2 in the flora): sc United States.
The basionym of Mentzelia humilis is often cited as M. multiflora var. humilis A. Gray (1852). However, in that publication Gray indicated accepted names in Roman capitals (see ipni.org), whereas the varietal name is in lower case, indicating that he was using it as a descriptive term rather than a scientific name. Valid publication of the basionym thus must be attributed to Urban and Gilg.