Virginia buttonweed

Diodia virginiana, the Virginia buttonweed, is a low-growing, mat-forming perennial herb of the Rubiaceae native to the southeastern and central United States and Mexico, with prostrate to ascending stems 20-80 cm long that often root at the lower nodes. The stems are quadrangular in cross-section, branched and glabrous to shortly pubescent in two longitudinal lines. Leaves are opposite, sessile or nearly so, narrowly lanceolate to oblanceolate, 2-7 cm long and 4-15 mm wide, with entire scabrous margins, an acute apex and a tapered base; interpetiolar stipules are fused into a short sheath bearing several slender bristles. The flowers are solitary or paired in the leaf axils, sessile, with a slender white to pale lilac corolla 6-10 mm long divided into four spreading lobes about as long as the tube. The calyx has four narrowly lanceolate, persistent lobes that enlarge in fruit. The fruit is a hard, ellipsoid, ribbed, hairy schizocarp 5-8 mm long that splits into two indehiscent one-seeded mericarps. The species grows in ditches, lawns, wet pastures, pond margins and disturbed moist soils.