Herbs, annual. Stems erect, 30–120 mm, minutely glandular-puberulent. Leaves basal and cauline, relatively even-sized; petiole absent; blade narrowly elliptic to oblanceolate, ovate, obovate, or elliptic-lanceolate, (1–)3–30(–50) × (0.4–)0.7–8(–20) mm, margins entire, plane, apex rounded or obtuse, surfaces minutely 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, 6–9 mm, minutely glandular-puberulent, lobes subequal, apex acute-apiculate, acuminate, or attenuate, ribs dark green or reddish, intercostal areas whitish. Corollas magenta to purplish, dark line often extending onto each abaxial lip lobe from throat, palate ridges yellow with red-purple speckling and border, throat floor villous with hairs extending onto abaxial lip, tube 1.1–1.9 mm diam. at filament insertion, tube-throat 11–15 mm, limb 8–14 mm diam., usually, rarely not, bilabiate. Anthers included or exserted, ciliate. Styles glandular-puberulent or glandular-pubescent. Stigmas exserted, lobes equal. Capsules 8–12 mm. 2n = 16.
Phenology: Flowering (Apr–)May–Jul.
Habitat: Openings in sagebrush, disturbed slopes, granite outcrops.
Elevation: (300–)1100–2300(–2900) m.
Calif., Idaho, Mont., Nev., Oreg., Wash., Wyo.
Diplacus nanus is broadly distributed through northern California, southern Idaho, and eastern Oregon, with stations in Ravalli County, Montana, and Park County, Wyoming, and scattered localities in Washington.
Diplacus nanus is generally recognized by its strongly bilabiate corollas with purplish (not yellow) tubes and two dark purple patches along the sides of the throats. The glandular-puberulent vestiture of D. nanus contrasts with the glandular-pubescent and viscid-villous vestiture (with hairs much longer) of D. mephiticus.
W. L. Ezell (1971) noted that in the Siskiyou Mountains of Josephine County, Oregon, and adjacent Siskiyou and Trinity counties, California, corollas of Diplacus nanus do not have clearly differentiated abaxial and adaxial lips.