Phytoneuron 2012-39: 32. 2012.
Herbs, annual. Stems erect, 3–40 (–80) mm, glandular-puberulent and/or glandular-pubescent. Leaves usually basal, reduced distally; petiole absent, larger with petiolelike extension; blade obovate to elliptic, 5–28 (–35) × (2–) 3–10 (–12) mm, margins entire or crenate, plane, not ciliate, apex obtuse, surfaces: proximals glabrate, distals glandular-pilose adaxially. Pedicels (1–) 2–4 mm in fruit, usually twisting to invert calyx. Flowers 2 per node, or 1 or 2 per node on 1 plant, chasmogamous or cleistogamous. Calyces distinctly asymmetrically attached to pedicel, not inflated in fruit, (6–) 8–14 (–15) mm, sparsely glandular-pilose, lobes subequal, apex appearing acute due to their continuity with ribs, ribs green to purplish, intercostal areas whitish. Corollas: throat magenta to dark purple, inside with longitudinal gold markings basally, adaxial lip magenta, palate ridges golden yellow, tube-throat (15–) 20–41 (–45) mm, limb 10–14 mm diam., abaxial lip essentially absent. Anthers (distal pair) nearly exserted, glabrous or glabrate. Styles pubescent distally. Stigmas exserted, lobes unequal, abaxial 10–20 times adaxial. Capsules (2.5–) 3–6.5 mm. 2n = 18.
Phenology: Flowering Feb–Apr(–May).
Habitat: Gentle to moderately steep slopes, upper banks of small creeks and ditches.
Elevation: 50–1200 m.
Diplacus douglasii occurs in southwestern Oregon and the northern two-thirds of California.
Diplacus douglasii is distinct in the complete or nearly complete lack of abaxial corolla lobes. Diplacus brandegeei, D. congdonii, D. kelloggii, and D. traskiae, the other species of sect. Cleisanthus, also show a distinct tendency toward reduction of the abaxial corolla lobes, and all species of the group except D. brandegeei produce markedly elongate corolla tubes.