Herbs, annual, usually acaulescent. Stems erect, 5–12(–20) mm, glandular-puberulent. Leaves basal or basal and cauline, relatively even-sized; petiole absent; blade narrowly elliptic to oblanceolate, 2–15 × 0.5–3.5 mm, margins entire or toothed, plane, proximal 1/2 usually ciliate, apex rounded, surfaces glandular-puberulent. Pedicels 0–1 mm in fruit. Flowers 1 per node, usually 1–5 per plant, chasmogamous. Calyces slightly asymmetrically attached to pedicel, inflated in fruit, 3.5–8 mm, glandular-puberulent, lobes subequal, apex rounded, ribs reddish purple, intercostal areas white. Corollas: throat, limb, and palate ridges yellow, central abaxial lobe and throat floor sparsely red-spotted, tube-throat 5–10 mm, limb 2–5 mm diam., bilabiate. Anthers included, glabrous. Styles sparsely glandular-puberulent distally. Stigmas usually exserted, lobes subequal. Capsules 2–4 mm, indehiscent. 2n = 20.
Phenology: Flowering May–Jun.
Habitat: Vernally flooded swales, mud flats flanking streams, stream banks, low spots in meadows.
Elevation: 1100–1800 m.
Diplacus pygmaeus occurs in northeastern California and south-central Oregon.