Plants perennial, rhizomatous; taproot stout, rhizomes thin, branching. Flowering shoots 4-10(-15) cm, softly pubescent. Leaves: cauline in 4-8 pairs, crowded; blade gray-green, oblanceolate to obovate, spatulate, 2.5-4.5 cm × 5-15 mm, longest near middle of stem, sparsely pubescent on both surfaces, reduced and bractlike on subterranean base. Inflorescences terminal, 1-3(-4)-flowered cymes, densely glandular-pubescent; bracts leaflike, (0.5-)0.7-1.1 cm. Pedicels ascending and straight, (5-)7-10 mm, glandular-pubescent. Flowers ca. 30 mm diam.; calyx purple tinged, distinctly 10-veined, tubular, inflated and expanding in fruit, 13-17 mm, densely glandular-pubescent, lobes lanceolate; corolla scarlet, clawed, limb carmine red, turning purple on drying, ± equally deeply 2-lobed, each lobe with lateral tooth, ca. 11 mm, glabrous, claw narrowly obtriangular, equaling calyx, appendages 2, prominent, petaloid, linear, truncate, 2.5-4.5 mm; stamens long-exserted; stigmas 3, long-exserted. Capsules ovoid to oblong, equaling calyx, (8-)12-15 mm; carpophore 0.5-1 mm. Seeds dark brown, reniform, 1.8-2 mm diam., strongly papillate. 2n = 72.

Flowering early summer. Grassy, gravelly, or rocky openings in chaparral, woodlands, and coniferous forest on serpentine; of conservation concern; 100-800 m; Calif.

Silene serpentinicola is a recently described endemic of the serpentines of the Smith River basin of northwestern Del Norte County and probably occurs on the same rock system across the border in Oregon. It differs from S. hookeri in flower color, and from both S. hookeri and S. laciniata subsp. californica in its erect, more or less solitary flowering stems and large, clearly visible petaloid appendages in the flowers.