Plants annual, glabrous or glan-dular-pubescent. Stems ascending or decumbent, frequently purple tinged, few- to many-branched, filiform. Leaves: axillary fascicles absent; basal rosette quickly de-ciduous; proximal cauline leaves connate basally, not appearing inflated, blade frequently purple tinged, linear, 4-23 mm, not fleshy, base never ciliate, margins conspicuously hyaline basally, apex apiculate, glabrous, distal blades becoming subulate and shorter toward apex, 1-5 mm, apex apiculate, glabrous. Pedicels filiform, glabrous or glandular-pubescent. Flowers terminal or often axillary, 5-merous, rarely 4-merous and then apetalous; calyx base glabrous or glandular-pubescent, often sparsely so; sepals ovate to orbiculate, (1-)1.5-2(-3) mm, hyaline margins conspicuous, margins or apex frequently purple, apex acute to rounded, glabrous or glandular-pubescent at calyx base, remaining appressed to capsule; petals elliptic, (1-)1.5-2(-2.3) mm, slightly longer than sepals at anthesis, equaling or shorter than sepals during capsule development; stamens 5 or 10, occasionally 8. Capsules 2-3(-3.5) mm, longer than sepals, dehiscing to 2 capsule length or less. Seeds light tan to light brown, obliquely triangular with abaxial groove, (0.2-)0.3-1.4 mm, smooth or pebbled to strongly tuberculate, protrusions sometimes borne on delicate ridges, ridges forming reticulate pattern (50-80×).
Slender, branching annual, ascending or decumbent, 3-10(-15) cm, often with short sterile axillary shoots; fls terminating the slender branches, commonly some also on slender, axillary glabrous pedicels 10-15 mm; sep 5(4), 1.5-2 mm, often purple-tipped or -margined; pet to ca as long as the sep, or wanting; stamens as many as the sep, or to twice as many; fr 2-3 mm, ellipsoid, evidently surpassing the erect-appressed sep; seeds light brown, 0.25-0.3 mm, flattened, obliquely triangular, sulcate along the 2 dorsal angles, very minutely glandular-tuberculate or essentially smooth; 2n=36. Wet places or dry, sandy soil; Mass. to Ill., s. to Fla. and Tex. Mar.- May. The apetalous form has been called var. smithii (A. Gray) S. Watson. S. occidentalis S. Watson, of Wash., Oreg., and Calif. is scarcely different from S. decumbens.
Gleason, Henry A. & Cronquist, Arthur J. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. lxxv + 910 pp.