Bot. Mag. 42: plate 1760. 1815.
Plants perennial, with caudices. Stems erect, to 50 cm. Leaves: petiole to 3 mm (proximal leaves), absent (distal leaves); blade ovate to hastate, rarely elliptic, basally lobed or unlobed, to 10 × 5 cm, base usually cuneate to truncate, sometimes acute, margins usually serrate, sometimes crenate, rarely entire, apex acute. Pedicels (fruiting) 0–2.5 × 2 mm. Flowers: petals orange, (6–)8–18.5 × (3–)4–10.5 mm, apex cuspidate, hairy abaxially on distal 1/2; stamens 15–45, 5–9.5 mm, filaments monomorphic, filiform; styles 5–10 mm. Capsules subcylindric to clavate, (5–)7–17 × 2–3.5 mm, base tapering gradually, capsule and pedicel not well-differentiated, walls thick, woody. Seeds (1–)2–3(–4) per capsule, oblong, without transverse folds. 2n = 20, 22.
Phenology: Flowering Mar–Oct.
Habitat: Limestone, gypsum, or sandstone rock outcrops or cliffs, clay or loam flats, grasslands, savannas.
Elevation: 0–1800 m.
Ariz., Ark., Colo., Ill., Kans., Mo., Nebr., N.Mex., Okla., S.Dak., Tex., Wyo.
After Mentzelia aspera, M. oligosperma may be the most widespread member of sect. Mentzelia. Occurring widely across the Great Plains, it also extends eastward into Missouri and western Illinois and across southwestern New Mexico into southeastern Arizona.