Herbs, annual. Stems erect, 10–150 mm, minutely glandular-puberulent. Leaves usually cauline, relatively even-sized; petiole absent; blade narrowly elliptic-oblanceolate to narrowly oblanceolate, 6–22 × 1–5(–7) mm, margins entire, plane, apex acute to obtuse, surfaces glandular-puberulent to glandular-pubescent. Pedicels 1 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, 3–5 mm, minutely puberulent, lobes subequal, apex acute to acuminate, ribs dark green to purplish, intercostal areas whitish. Corollas lavender-purple to rose purple, throat darker, palate ridges yellow, red-spotted, tube 0.8–1.2 mm diam. at filament insertion, tube-throat 7–10 mm, limb 5–7 mm diam., bilabiate. Anthers exserted, sparsely hispidulous. Styles glandular-puberulent or glandular-pubescent. Stigmas exserted, lobes equal. Capsules 4–6 mm. 2n = 16.
Phenology: Flowering Jun–Aug.
Habitat: Gentle slopes, sandy and volcanic soils, meadows in spruce-fir forests, openings among pines and in chaparral, shallow drainage areas, disturbed open areas.
Elevation: (900–)1100–2500(–2800) m.
Calif., Nev., Oreg.
D. M. Thompson (2005) treated Diplacus jepsonii as conspecific with D. nanus [as W. L. Ezell (1971) had done earlier] because of putative intergrades. In its typical form, D. jepsonii is immediately distinct in its narrower leaves, stems with well-separated proximal nodes, and smaller corollas with nearly filiform tubes. R. J. Meinke (1992), in a field and greenhouse study not cited by Thompson, found that D. jepsonii and D. nanus are distinct in morphology as well as in habitat and that the two do not grow intermixed in nature.
Diplacus jepsonii is known only from north-central California, southern Washoe County, Nevada, and southern Oregon. Putative outliers in the central Sierra Nevada are dubiously identified.