Plants loosely cespitose or with solitary stems; rhizomes horizontal, purple to black, 25-75(-100) mm, slender. Culms 8-38 cm; bases (remnants of old leaves) weakly to strongly fibrous. Leaf blades green, 1.5-3.5(-5) mm wide, herbaceous, smooth to scabrous abaxially, smooth to scabrous adaxially. Inflorescences usually with either staminate or pistillate spikes, occasionally with both; peduncles of staminate spikes short; proximal nonbasal bracts leaflike, dark purple to black at base, shorter than inflorescences. Spikes: proximal pistillate spikes 1-4 (basal spikes 0-1); cauline spikes overlapping or somewhat separted, with 4-9 perigynia; staminate spikes 13-24 × (1.4-)2-4.1 mm. Scales: pistillate scales dark purple to black, with narrow white margins, lanceolate, 3.8-4.6 × 1.3-1.8 mm, apex acuminate; staminate scales oblanceolate, 4.6-5.6 × 1.1-1.6 mm, apex acute; proximal staminate scales with narrow white margins 0.1-0.2 mm wide. Anthers 2.1-4 mm. Perigynia green, occasionally dark purple in age, veinless or 5-veined near base, obovoid, 3.1-3.6 × 1.5-1.8 mm; beak slightly bent, dark purple, 0.5-1 mm, weakly ciliate-serrulate, apical teeth 0.2 mm. Stigmas 3. Achenes pale to medium brown, globose, round in cross section, 1.9-2.2 × 1.4-1.8 mm.

Fruiting mid Apr-mid Jun. Open or partly shaded, vernally moist to wet meadows, riparian woodlands, savannas, successional scrublands, wetland margins, serpentine soils derived from ultramafic bedrock; 60-1200 m; Calif., Oreg.