Plants annual; taproot slender. Stems straggling to ascending, branched, square, 10-25 cm, glabrous. Leaves sessile; blade with obscure midrib, narrowly oblanceolate to linear-spatulate, 1-3 cm × 0.8-4 mm, somewhat fleshy, base cuneate, margins entire, apex ± acute, glabrous. Inflorescences with flowers solitary in distal leaf axils; bracts absent. Pedicels ascending or erect, 10-40 mm, glabrous. Flowers 2.5-4 mm diam.; sepals 4(-5), 3-veined, ovate-lanceolate, 2.5-3 mm, margins narrow, scarious, apex ± acute, glabrous; petals absent; stamens 4(-5), shorter than sepals; styles 3 or 4, ascending, ca. 0.5 mm. Capsules green or straw colored, ovoid, ca. 3 mm, ± equaling sepals, apex obtuse, opening to base into 3 or 4 valves; carpophore absent. Seeds dark red-brown, orbiculate-reniform, 0.6 × 0.8 mm, shiny, tuberculate; tubercles prominent, stalked and knoblike.

Flowering spring. Seasonally wet, rocky openings in wooded glades, on wet cliffs; 400-500 m; Ky., Tenn.

Stellaria fontinalis is a very rare and poorly known species of uncertain affinity. Its characters are closer to Sagina and Minuartia than Stellaria, in particular the absence of petals, the 4(-5)-merous flowers, and the distinctive sculpturing of the seeds.