Herbs, annual, winter-annual, or perennial, often cespitose or matted. Taproots slender. Stems ascending, decumbent, or procumbent, simple or branched, terete to slightly angular. Leaves: basal and secondary rosettes present in perennial species, usually connate proximally, sometimes forming conspicuous, scarious cup, sessile, with or without axillary fascicles of leaves; blade 1-veined, linear to subulate, succulent or not, apex acute to mucronate or apiculate (or long-aristate in S. subulata). Inflorescences terminal or axillary cymes, or flowers solitary; bracts paired, foliaceous. Pedicels erect or spreading. Flowers: perianth and androecium hypogynous; sepals 4 or 5, distinct, green or sometimes purple (in S. nivalis and S. decumbens), lanceolate to elliptic or orbiculate, 1-5.5 mm, herbaceous, margins white or purple, scarious, apex obtuse or rounded to somewhat acute, frequently hood-shaped in bud; petals 4 or 5, sometimes absent (frequently absent or soon dropping in annual species), white, claw absent or minute, blade apex entire; nectaries at base of filaments opposite sepals; stamens 4, 5, 8, or 10, arising from base of ovary; filaments distinct; staminodes absent; styles 4 or 5, clavate to filiform, 0.5-1.5 mm, glabrous proximally; stigmas 4 or 5, subterminal to linear along adaxial surface of styles, minutely papillate (30×). Capsules globose to ovoid, opening by 4 or 5 valves, sutures running to base, but in some species dehiscing only ca. 1/ 1/ 2 capsule length; carpophore absent. Seeds ca. 125, light tan to dark or reddish brown, obliquely triangular with abaxial groove, or reniform to nearly globose without abaxial groove (except S. nodosa, which is intermediate), laterally compressed or plump, smooth to tuberculate, marginal wing absent, appendage absent. x = 6, 7, 11.
Fls solitary and terminal or axillary , or in terminal cymes; sep mostly 5 or 4; pet as many as the sep, white, entire or emarginate, or none; stamens as many as and opposite the sep, or twice as many; styles as many as and alternate with the sep; valves of the capsule opposite the sep; seeds numerous, minute; low, matted, delicate annuals or perennials with opposite, basally connate, narrow (often linear-subulate) lvs, lacking stipules. 15, mostly cold-temp. N. Hemisphere.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.