Rhizomes with ± vertical, fleshy roots 5-15 cm × 0.3 mm, enlarging distally to 2-3 mm diam. Stems terete, obtusely angled or grooved when pressed, 9-27 cm, glabrous. Leaf blades narrowly lanceolate or elliptic, 0.7-3.5 × 0.1-0.5(-0.8) cm, margins flat, thinly scarious, smooth, glabrous. Inflorescences terminal, solitary flowers, sometimes on 1-2 axillary branches. Pedicels abruptly bent downward near distal end in fruit, glabrous. Flowers: sepals lanceolate to narrowly ovate, 4-6.5(-7) × 1-1.7 mm, glabrous; petals 5-8(-9) × 1-1.5 mm, apex notch 0.2-0.7 mm deep, lobes ± acute; anthers 5, yellow; styles 2-3.5 mm; stigmas terminal, 0.1-0.2 mm. Capsules 4-4.5 mm. Seeds 1(-2), light brown, circular to somewhat oblong, flattened laterally, 3-3.4 mm; tubercles broadly conic to elongate, rounded, each with 6-12 minute, red bumps that develop into 5-8 conic projections ca. 0.02 mm (50×).

Flowering summer. Dry understory of mixed oak or coniferous forests; of conservation concern; 1400-2000 m; Calif.

First collected in the 1880s, Pseudostellaria sierrae appears to be limited to the northern High Sierra region (J. C. Hickman 1993b).