Herbs, annual. Stems erect to ascending, 10–140 mm, glandular-puberulent to short glandular-villous. Leaves usually cauline, relatively even-sized; petiole absent; blade oblanceolate to linear, (5–)6–24(–34) × (0.5–)1–4(–7.5) mm, margins entire, plane, apex rounded to acute, surfaces glandular-puberulent. Pedicels 1(–3) mm in fruit. Flowers 2 per node, or 1 or 2 per node on 1 plant, chasmogamous. Calyces symmetrically attached to pedicels, not inflated in fruit, (2.5–)3–5.5(–6.5) mm, glandular-puberulent, lobes subequal, apex acute, ribs darkened, blackish, intercostal areas purplish. Corollas magenta, sometimes white, throat whitish, often speckled with dark spots, palate ridges weak, whitish to pinkish, tube-throat 6–8 mm, limb 3–5 mm diam., not bilabiate. Anthers included, glabrous. Styles sparsely glandular-puberulent. Stigmas included, lobes unequal, abaxial nearly 2 times adaxial. Capsules (3–)4–6(–6.5) mm. 2n = 16.
Phenology: Flowering Jun–Aug.
Habitat: Developing granitic soils, boulders of granite outcrops, disturbed areas, water runoff areas.
Elevation: (1800–)2100–3400 m.
Diplacus leptaleus occurs in the Sierra Nevada from Nevada County south to Tulare County, California, and in southern Washoe County, Nevada. Diplacus leptaleus is the only species of Diplacus that commonly produces white flowers. Populations rarely are fixed for white corollas; they are commonly fixed for magenta corollas, especially at higher elevations (D. M. Thompson 2005).