Herbs, annual. Leaves: basal rosette present, not persistent, proximalmost internodes to 10+ mm; blade without broad basal lobes, margins toothed to pinnate, flat. Flowers: stamens all fertile or 1–3(–5) outermost sterile, filaments dorsiventrally flattened, ±monomorphic, linear, or heteromorphic, 1–3(–5) outermost oblanceolate, petaloid, inner linear, distally 2-lobed or unlobed; ovules (and seeds) oriented perpendicular or ± parallel to long axis of ovary. Capsules cup-shaped, cylindric, or ovoid, straight. Seeds pyriform to ovoid and flattened dorsiventrally, not winged; seed coat cells polygonal, ± isodiametric, anticlinal walls straight or wavy.

Distribution

sw United States, nw Mexico.

Discussion

Species 5 (5 in the flora).

Selected References

Daniels, G. S. 1970. The Floral Biology and Taxonomy of Mentzelia Section Bicuspidaria (Loasaceae). Ph.D. dissertation. University of California, Los Angeles.

Lower Taxa

Mentzelia hirsutissima, Mentzelia involucrata, Mentzelia reflexa, Mentzelia tricuspis, Mentzelia tridentata

Key

1	1–3(–5) outermost stamens staminodial and petaloid (flowers appearing to have 6–8(–10) petals); stamen filaments unlobed; petals lanceolate to oblanceolate, 6–12 mm, apices acute; styles 5–6.5 mm.	Mentzelia reflexa
1	Stamens all fertile, none petaloid (flowers appearing to have 5 petals); stamen filaments all or most distally 2-lobed; petals obovate, 10–65 mm, apices mucronate; styles 6–30 mm.	> 2
2	Bracts conspicuous, concealing pedicels, ovaries, and capsules, white with green margins.	Mentzelia involucrata
2	Bracts inconspicuous, not concealing pedicels, ovaries, or capsules, green.	> 3
3	Stamen filament lobes 0.6–2.5 mm, anther stalk usually shorter; seeds constricted and grooved at middle.	Mentzelia tricuspis
3	Stamen filament lobes 0.1–0.7 mm, anther stalk equal or longer; seeds widest at middle, not grooved.	> 4
4	Petioles absent in cauline leaves, blade base often cordate-clasping; capsules erect; far southwestern Sonoran Desert.	Mentzelia hirsutissima
4	Petioles present in distalmost cauline leaves, blade base not cordate-clasping; proximal capsules nodding, distal erect; central Mojave Desert.	Mentzelia tridentata