Diodia virginiana aka Virginia Buttonweed

Diodia virginiana is best known as Virginia buttonweed. It belongs to the coffee family, Rubiaceae. Its native range spans the central and eastern United States. It also reaches central Mexico and Cuba. It grows in marshes, wet meadows, swamps, and coastal prairies. Muddy banks of streams and ponds also suit it. Though troublesome in southern lawns, it is rare in New Jersey and Indiana.

This warm-season herb forms thick mats close to the ground. NC State describes it as perennial; Kew lists it as annual. It has deep roots and underground stems called rhizomes. Stems can reach 2 feet [0.61 metres] from the woody root. They may take root where their nodes touch soil. Green or reddish stems have square or many-angled sections. Their edges may be smooth or bear ridges and hairs. Seeds and broken stem pieces both help it spread.

Pairs of green leaves grow straight from the stems without stalks. Each simple, lanceolate leaf has smooth edges and a pale underside. Leaves reach about 0.21 feet [0.064 metres] long. Hairy stipules form a sheath where the leaves meet the stem. Small white flowers open from June through November. Each tube ends in four lobes that spread like a star. Some flowers have pink lines near the centre. Blooms grow alone or in pairs at the leaf joints. The green, hairy fruit has a tough outer wall. Each oval capsule holds two seeds and splits when ripe.

The plant grows in full sun or partial shade. It prefers moist to wet ground but accepts varied soils. These include clay, loam, and soil rich in organic matter. It also tolerates poor soil and grows at a moderate rate. NC State lists it for USDA zones 6a through 9b. Its long bloom season draws bees. Underwater stems shelter small animals that fish and other wildlife eat. Decaying plants also feed aquatic invertebrates.

Its spread makes it a poor choice for home gardens. Dense mats can crowd out other plants and invade lawns. Deep roots and several means of spread make removal hard. It hosts flea beetles, which may harm nearby garden plants. A virus can cause yellow patches on the leaves. A healthy lawn can help limit its spread. Control work starts as shoots emerge in early spring. The supplied sources give no food uses or toxicity findings.