Plants perennial, cespitose, frequently forming dense mats or tufted, glandular-pubescent or glabrous. Stems ascending or decumbent, few-branched, not filiform, densely glandular-pubescent, or less frequently glabrous; horizontal stems becoming slightly woody with extensive mat formation. Leaves: axillary fascicles absent; basal forming tufts, blade linear, curled inward, 3-12 mm, not fleshy, apex long-aristate, aristae equaling or exceeding leaf width, densely glandular-pubescent, or with glandular hairs restricted to margins, and then often minutely glandular-ciliate, rarely glabrous; cauline connate basally, forming conspicuous cup, blade linear-subulate, 3-10 mm, scarious. Pedicels filiform, densely to weakly glandular-pubescent. Flowers axillary or terminal, usually solitary, 5-merous, rarely 4- and 5-merous; calyx bases glandular-pubescent; sepals elliptic, 1.5-2 mm, hyaline margins white, apex obtuse to rounded, glandular-pubescent, remaining appressed following capsule dehiscence; petals elliptic, 1.5-2 mm, shorter than or equaling sepals; stamens (8 or) 10. Capsules 2-3(-3.5) mm, slightly longer than sepals, dehiscing to base. Seeds brown, obliquely triangular with abaxial groove, 0.4(-0.5) mm, smooth. Flowering mid-late summer. Wet, gravelly sands of stream margins; 0-1800 m; introduced; Oreg.; Mexico (Baja California Sur); Europe. Three specimens from the alpine zone of Steens Mountain, Harney County, are referable to Sagina subulata. Introduction of the species into that remote area is without explanation.
A strongly mat-forming cultivar of Sagina subulata is sometimes grown as a ground cover; plants flower profusely, but no subsequent capsule development typically occurs. The cultivar differs from the native European mat-forming plants by being glabrous except for the minutely glandular-ciliate leaf margins. Occasional waifs have been collected in the San Francisco area of California.