Plants annual, delicate, 5-15 cm, stipitate-glandular throughout or nearly so. Taproots slender. Stems erect to diffusely spreading, much-branched proximally and distally; main stem 0.3-0.7 mm diam. proximally. Leaves: stipules inconspicuous, silvery to dull tan, broadly triangular, 1.5-2 mm, apex acuminate; blade linear, 0.6-2.3 cm, somewhat fleshy, apex blunt to apiculate; axillary leaf cluster usually absent. Cymes simple but commonly 4-8+-compound. Pedicels erect to reflexed in fruit. Flowers: sepals connate 0.2-0.5 mm proximally, lobes 1-veined or not, lanceolate to ovate, 2.3-3.1 mm, enlarging little in fruit, margins 0.1-0.3 mm wide, apex obtuse to rounded; petals white, elliptic to ovate, 0.7-0.8 times sepals; stamens 4-7; styles 0.4-0.6 mm. Capsules greenish tan, 2.5-2.8 mm, 0.9-1.2 times sepals. Seeds black, often with silvery, not iridescent tinge, with submarginal groove, pyriform, somewhat compressed, 0.4-0.6 mm, shiny, sculpturing of low, elongate tubercles, not papillate (40×); wing absent. 2n = 18 (Europe).
Flowering spring-fall. Sandy beaches, river shores; 600-700 m; introduced; Alta., B.C., Sask.; Idaho, Mass., Oreg., Wash.; Europe (Mediterranean region); sw, c Asia; n Africa; introduced in Australia.
R. P. Rossbach's (1940) report of Spergularia diandra from Georgia is referred to 9. S. echinosperma.
The name Spergularia diandra was effectively and validly published via an autographic label distributed in 1851, predating the other commonly seen attributions of this combination.