Herbs, annual, herbage usually drying dark. Stems erect, 60–120(–150) mm, nodes 4–15(–20), internodes shorter than leaves, glandular-villous with gland-tipped hairs 1–1.6 mm. Leaves usually cauline, relatively even-sized; petiole weakly delimited; blade usually lanceolate to ovate-lanceolate, 20–40 × 4–12 mm, margins entire, rarely toothed, plane, apex rounded to obtuse or acute, surfaces: proximals often glabrate abaxially, distals glandular-villous. Pedicels 1–3 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, 8–12 mm, glandular-villous, tube strongly plicate, lobes triangular, subequal, apex acute, ribs narrow, darkened, blackish, thickened, strongly raised, intercostal areas green to purple, not membranous. Corollas nearly white or pale lavender to pinkish or pale to dark magenta, each lobe with a dark medial line extending nearly to tip, throat with a dark red or purple splotch at junction of each abaxial lobe and adjacent lateral lobe, throat floor sometimes with 2 adjacent white splotches at lateral lobe bases, palate ridges yellow, tube-throat 15–20 mm, limb 10–16 mm diam., bilabiate. Anthers included, ciliate. Styles glandular-puberulent. Stigmas included, lobes unequal, abaxial 1.5 times adaxial. Capsules 6–10 mm. 2n = 16.
Phenology: Flowering Apr–Sep.
Habitat: Granite cracks and crevices.
Elevation: 300–2100 m.
Diplacus graniticola occurs in the Sierra Nevada from Tuolumne County to northern Tulare County. These plants previously were identified within D. layneae, with which they are partially sympatric; where these two occur together, D. layneae often grows in granite-derived sand and gravel immediately adjacent to the granite rock habitat of D. graniticola.