Herbs, annual. Stems erect to erect-ascending, (10–)30–240(–350) mm, distal internodes 1–5 mm, densely glandular-villous. Leaves basal and cauline or usually cauline, relatively even-sized or gradually larger distally; petiole absent, proximal base short petiole-like, 1–5 mm; blade ovate to broadly elliptic-ovate, (10–)15–25(–35) × 4–16 mm, margins entire, plane, apex abruptly acuminate, surfaces densely glandular-villous. Pedicels 1–1.5 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, 7–12 mm, glabrous or minutely stipitate-glandular, lobes unequal, apex linear-acuminate, sharp-pointed, ribs green distally, intercostal areas whitish. Corollas magenta or rose purple, tube yellow, throat usually yellow, throat and distal tube red-spotted on floor, palate ridges yellow, tube-throat 13–16(–19) mm, limb 14–26 mm diam., bilabiate. Anthers included, glabrous or sparsely hirsutulous. Styles puberulent, at least on distal 1/2. Stigmas exserted, lobes subequal (herkogamous). Capsules 10–17 mm.
Phenology: Flowering May–Aug.
Habitat: Lava formations, steep slopes, roadsides, volcanic gravels, scree, ash.
Elevation: (400–)600–1500(–2000) m.
Calif., Idaho, Oreg., Wash.
Diplacus cusickioides occurs in western Idaho, eastern Oregon, Klickitat County, Washington, and apparently in a disjunct population system in Modoc County, California, on the east side of the Warner Mountains.