Plants 5–30 cm. Basal leaves: petioles present; blade lanceolate, to 12 cm; margins shallowly lobed, lobes rounded. Cauline leaves: petioles usually present, rarely absent; blade broadly ovate to lanceolate, to 12 cm, base not cordate-clasping, margins dentate to serrate. Bracts green, inconspicuous, not concealing pedicel, ovary, or capsule. Flowers: petals white to pale yellow, obovate, 10–30(–50) mm, apex mucronate; stamens 7–17 mm, less than 1/2 petal length, all fertile, none petaloid (flowers appearing to have 5 petals); filaments ± monomorphic, linear, distally 2-lobed, lobes 0.6–2.5 mm; anther stalk usually shorter than filament lobes; style 10–15 mm. Capsules cylindric to ovoid, 9–18(–23) × 5–8 mm, proximal nodding, distal erect. Seeds constricted and grooved at middle; seed coat anticlinal cell walls straight to slightly wavy, conspicuous. 2n = 20.
Phenology: Flowering Mar–May.
Habitat: Sandy or gravelly slopes, washes, desert scrub.
Elevation: 150–1300 m.
Ariz., Calif., Nev.
Mentzelia tricuspis is morphologically most similar to M. tridentata with differences largely limited to the lengths of the stamen filament lobes (and thus relative lengths of the anther stalks) and shapes of the seeds. However, the species are also distinct geographically, with M. tricuspis found in the southeastern Mojave Desert and northwestern Sonoran Desert and M. tridentata in the central to western Mojave Desert.