Oenothera exilis P. H. Raven, Univ. Calif. Publ. Bot. 34: 114. 1962; Camissonia exilis (P. H. Raven) P. H. Raven

Herbs annual, glandular puberulent and sparsely villous. Stems slender, unbranched or branched, 10–20 cm. Leaves primarily cauline; petiole 0.3–1.8 cm; blade unlobed, narrowly ovate to elliptic, 0.3–2 × 0.3–1 cm, margins entire or inconspicuously denticulate, brownish oil cells lining veins abaxially. Racemes erect, elongating in fruit. Flowers opening at sunrise; buds without free tips; floral tube 0.4–0.5 mm, glabrous inside; sepals 1–1.2 mm; petals yellow, fading pale lavender, 1–1.5 mm; stamens 4 (or 8), antisepalous, filaments 0.5 mm, anthers 0.5–0.7 mm, glabrous, when 8, then antipetalous ones smaller and abortive; style 1.5 mm, stigma surrounded by anthers at anthesis. Capsules spreading or reflexed, clavate, 4–10 mm; pedicel 3–9 mm. Seeds 0.8 mm. 2n = 14.

Flowering Apr–Jun. Calcareous sand, gypseous clay flats, juniper woodlands; of conservation concern; 1000–1900 m; Ariz., Utah.

Chylismia exilis, known from Kane and San Juan counties in Utah and northern Coconino and Mohave counties in Arizona, is cryptic due to its small size. It may not be as rare as assumed, since it is difficult to spot in the field. P. H. Raven (1962, 1969) determined this species to be self-compatible and autogamous.