Subshrubs or shrubs. Stems erect to ascending-erect, 300–1200 mm, glabrous. Leaves cauline, relatively even-sized; petiole absent; blade elliptic to broadly elliptic-oblanceolate or elliptic-lanceolate, 15–60 × 4–21 mm, margins entire or serrate, plane or revolute, apex acute to obtuse or rounded, surfaces glabrous. Pedicels 6–15 mm in fruit. Flowers 2 per node, chasmogamous. Calyces not inflated in fruit, 18–25 mm, glabrous, tube slightly dilated distally, lobes unequal, apex acute, ribs green, intercostal areas light green. Corollas deep red to scarlet, throat sometimes orange, not spotted or striped, palate ridges red to orange-red, tube-throat 27–33 mm, limb 12–16 mm diam., bilabiate, lobes oblong, each truncate-entire to slightly emarginate. Anthers exserted, glabrous. Styles minutely glandular. Stigmas exserted, lobes equal. Capsules 14–21 mm. 2n = 20.
Phenology: Flowering Mar–Aug.
Habitat: Hillsides, canyons, rocky slopes and walls, bluffs, sea cliffs.
Elevation: 10–400 m.
Diplacus parviflorus is known from four of the Channel Islands (Anacapa, San Clemente, Santa Cruz, and Santa Rosa).
Hybrids with Diplacus longiflorus occur on Santa Cruz Island; A. L. Grant (according to label data of collections) found these to be fairly common on open hillsides near Friar’s Harbor and Valdez, where the two species grew near each other though apparently separated in habitat, with typical D. parviflorus mostly in the canyons and D. longiflorus on open hillsides. She noted that the apparent hybrids were variable in all possible combinations of features of the leaves, calyces, and corollas, including color.
Mimulus parviflorus (Greene) A. L. Grant 1925, not Lindley 1825, pertains here.