Oenothera heterochroma S. Watson var. megalantha Munz, Leafl. W. Bot. 3: 52. 1941; Camissonia megalantha (Munz) P. H. Raven; O. megalantha (Munz) P. H. Raven

Herbs annual, glandular pubes­cent throughout. Stems several, 10–200 cm. Leaves in poorly defined basal rosette and cauline; petiole 1.8–5.5 cm; blade unlobed, broadly cordate to ovate, 2.4–8 × 7 cm, margins sinuate-dentate, yellowish oil cells prominently lining veins abaxially. Racemes erect, elongating in flower. Flowers opening at sunrise; buds without free tips; floral tube 4–9 mm, with matted, villous hairs inside; sepals 4.5–9 mm; petals pale to dark lavender, diffusely purplish-flecked near base, white at very base, fading darker lavender, 9–14 mm; stamens unequal, filaments of antisepalous stamens 6–12 mm, of antipetalous ones 3.5–8 mm, anthers 2 mm, glabrous; style 14–22.5 mm, stigma exserted beyond anthers at anthesis. Capsules erect or ascending, clavate, 8–14 mm; pedicel 2–3.5 mm. Seeds 1–1.3 mm. 2n = 14.

Flowering Jun–Oct. Rubble derived from volcanic tuff, partly on moist soil along springs; 1200–1400 m; Nev.

Chylismia megalantha is known from around Frenchman Drainage to French Peak and Skull Mountain in southern Nye County. P. H. Raven (1962, 1969) determined this species to be self-compatible, but outcrossing.