Herbs, annual, herbage usually drying dark. Stems erect, (10–)20–240(–350) mm, nodes 3–6, internodes 1–6 mm, glandular-villous. Leaves basal and cauline, relatively even-sized; petiole indistinct; blade obovate, oblanceolate, or narrowly elliptic, (3.5–)5–32(–47) × 3–15(–18) mm, margins entire or toothed, plane, apex acute or rounded, surfaces: proximals glabrous, distals glandular-pubescent. Pedicels 0.5–3(–4) mm in fruit. Flowers 2 per node, or 1 or 2 per node on 1 plant, chasmogamous. Calyces symmetrically attached to pedicels, inflated in fruit, (5–)7–12(–15) mm, glandular-pubescent to glandular-villous, tube strongly plicate, lobes triangular, subequal, apex acute, ribs broad, darkened, blackish, thickened, strongly raised, intercostal areas whitish, membranous. Corollas magenta or pinkish to red-purple, throat floor whitish with dark lines or streaks, often yellowish deep inside throat, never at mouth, palate ridges white, tube-throat (10–)13–22(–25) mm, limb 14–23 mm diam., not bilabiate. Anthers included, ciliate. Styles glandular-puberulent. Stigmas included, lobes equal. Capsules (7–)8–12(–13.5) mm. 2n = 16.
Phenology: Flowering May–Aug.
Habitat: Disturbed areas with concentrated runoff from rains on, or just above, verges of roadside banks.
Elevation: 800–2100(–2400) m.
Diplacus constrictus is endemic to Kern, Los Angeles, Tulare, and Ventura counties.