Slender annual herb up to 40 cm high. Stems glabrous, simple to much-branched at base. Stem lvs always alternate, glabrous, narrowly elliptic-obovate to linear, usually narrow-obovate at base of stem, acuminate, 1-veined, entire, (1)-3-15-(20) mm long; lvs subtending infl.-branches single, lanceolate, < stem lvs. Infl. of few to numerous fls in a diffuse compound dichasium; sepals narrow-ovate, long-acuminate, often sparsely glandular, ciliate, 3-4 mm long, sometimes ± = but usually > capsule; petals yellow, somewhat > to almost 2× as long as sepals, 3.5-6 mm long; styles free ± to base. Capsule glabrous, subglobose, dehiscent, 2-2.5 mm diam.; seeds ± elliptic, shiny light brown, c. 1 mm long.