Herbs, annual. Stems erect, (30–)60–370 mm, densely glandular-pubescent with viscid hairs. Leaves usually cauline, relatively even-sized or largest proximally and gradually reduced distally; petiole absent; blade obovate to narrowly elliptic, (4–)8–54(–70) × (2–)3–23 mm, margins entire or serrate, plane, apex obtuse to rounded, surfaces: proximals glabrous abaxially, distals glandular-pubescent. Pedicels 1–4(–5) mm in fruit. Flowers 1 per node, chasmogamous. Calyces symmetrically attached to pedicels, inflated in fruit, (7–)8–15 mm, villous, hairs eglandular, lobes subequal, apex acute to attenuate, ribs and intercostal areas often reddish. Corollas lavender to magenta with diffuse dark markings on sides of darker tube-throat and with dark red-purple midveins on lobes extending from throat, lobes not dark at base, floor white or yellow, fading to white at mouth, palate ridges white or yellow fading to white distally, throat ceiling glabrous, tube-throat 10–20 mm, limb 8–20 mm diam., not bilabiate. Anthers included, ciliate. Styles glandular-puberulent. Stigmas included, lobes unequal, abaxial 1.5 times adaxial. Capsules 7–11 mm. 2n = 16.
Phenology: Flowering Apr–Jul.
Habitat: Chaparral clearings and openings.
Elevation: 90–1300 m.
D. M. Thompson (2005) noted that Diplacus viscidus and D. compactus (as Mimulus viscidus var. compactus) are parapatric and may intergrade in central Mariposa County. The two taxa are distinguished by the presence or absence of dark stripes on the corolla lobe midveins, which are evident even on herbarium specimens. Thompson found that the two remained distinct when grown together in the greenhouse.
Diplacus viscidus is known from Amador, Calaveras, Eldorado, Mariposa, Merced, and Tuolumne counties; D. compactus continues south through Fresno, northern Kern, Madera, Mariposa, and Tulare counties.