Oenothera pterosperma S. Watson, Botany (Fortieth Parallel), 112, plate 14, figs. 4–7. 1871; Camissonia pterosperma (S. Watson) P. H. Raven; Chylismia pterosperma (S. Watson) Small; Sphaerostigma pterospermum (S. Watson) A. Nelson

Herbs sparsely to moderately spreading hirtellous, becoming glandular puberulent distally. Stems slender, ascending, branching, 2–15 cm. Leaves 0.3–3 × 0.1–0.6 cm; petiole 0.2–0.7 cm; blade sometimes with purple spots, narrowly lanceolate to oblanceolate. Flowers opening at sunrise; floral tube 1–2 mm; sepals often reddish green, 1.5–2.5 mm; petals white with yellow area at base, broadly obovate, apex notched, 1.5–3 mm; episepalous staminal filaments 1–1.7 mm, epipetalous ones 0.5–1 mm, anthers 0.3–0.4 mm; style 2.2–4 mm, stigma 1–1.5 mm diam., surrounded by anthers at anthesis. Capsules ascending or spreading, 12–18 × 1.2–1.6 mm; pedicel 4–8 mm. Seeds 1–1.5 × 0.6–0.8 mm, broader at 1 end, ends truncate (where contacting next seed in row), clavate hairs longer at one end, shortest in middle. 2n = 14.

Flowering Apr–Jun. Well-drained slopes, often of volcanic origin, with sagebrush and pinyon-juniper; 700–2600 m; Ariz., Calif., Idaho, Nev., Oreg., Utah.

The range of Chylismiella pterosperma, an inconspicuous and uncommon plant, centers across Nevada and extends to southeast Oregon (Lake and Malheur counties), western Utah, northwest Arizona (Coconino and Mohave counties), eastern California (Inyo County), and southern Idaho (Butte County).