Phytoneuron 2012-39: 30. 2012.
Herbs, annual, acaulescent or caulescent. Stems erect, 0 or 20–70 mm, eglandular-puberulent. Leaves: basal densely clustered; petiole absent; blade narrowly lanceolate or elliptic to linear, (3.5–) 5–36 × 0.5–3.8 (–5) mm, margins entire, plane, proximal 1/2+ ciliate, apex obtuse, surfaces glabrous. Pedicels 0–1 mm in fruit. Flowers 1 per node, chasmogamous. Calyces slightly asymmetrically attached to pedicel, inflated in fruit, (4–) 7–14 (–17) mm, pilose, lobes subequal, apex obtuse, ribs becoming reddish, intercostal areas pale green to whitish. Corollas: throat and limb magenta to purple with a dark maroon-purple spot or elongate blotch at base of each abaxial lobe, palate ridges and base of abaxial lip yellow, tube-throat 20–60 mm, limb 10–20 mm diam., bilabiate, lobes equal. Anthers (distal pair) sometimes nearly exserted, hirsute with 2 apical tufts. Styles glandular-puberulent. Stigmas usually exserted, lobes subequal. Capsules 2–4.5 mm, indehiscent. 2n = 18.
Phenology: Flowering Mar–May(–Jun).
Habitat: Vernally flooded depressions or swales, summits of mesas or foothills.
Elevation: 300–1200 m.
Diplacus angustatus occurs in northern California in the Sierra Nevada and across the Sacramento Valley in the North Coast Range (Lake, Mendocino, and Napa counties); it also is known from one area in northwestern Shasta County and has a disjunct series of populations in Fresno and Tulare counties.