Herbs, annual. Stems erect to ascending, 20–140 mm, distal internodes 1–3 mm, glandular-pubescent and short glandular-villous. Leaves usually cauline, relatively even-sized or slightly reduced distally; petiole absent, base sometimes tapered to narrow, petiole-like extension; blade obovate to broadly oblanceolate, 13–33 × 5–12(–16) mm, margins entire, plane, apex acuminate, surfaces densely glandular-villous. Pedicels 2–3(–5) mm in fruit. Flowers 2 per node, or 1 or 2 per node on 1 plant, chasmogamous. Calyces symmetrically attached to pedicels, not inflated in fruit, 7–9(–10) mm, coarsely glandular-pubescent, lobes subequal, apex lanceolate to narrowly lanceolate, ribs purplish, intercostal areas white. Corollas magenta to red-purple with a yellow patch on palate, sometimes yellow with a red-brown patch, palate ridges orange-yellow, tube-throat 9–11 mm, limb 12–15 mm diam., bilabiate. Anthers exserted, sparsely hirsutulous. Styles glandular-puberulent. Stigmas exserted, lobes subequal. Capsules 6–8 mm.
Phenology: Flowering Apr–Jun(–Aug).
Habitat: Dry to moist, often barren, loose, sandy to gravelly slopes, andesite or rhyolite deposits, sandy alkaline valley floors, roadsides, washes, sagebrush, pinyon-juniper, open yellow pine woodlands.
Elevation: 1300–1900(–2400) m.
Mimulus ovatus was treated as a distinct species by N. H. Holmgren (1984); the plants were considered by D. M. Thompson (2005) to be hybrids between M. nanus var. mephiticus and M. cusickii, and he placed the name as a synonym of M. cusickii. Diplacus ovatus is known only from Carson City, Douglas, and southern Washoe counties.