Diodia virginiana

Also known as Buttonweed, Virginia Diodia

Virginia buttonweed forms low-growing, dense mats across moist lawns, meadows, and muddy riverbanks. Small white, star-shaped flowers with four petals bloom throughout summer, tucked tightly into leaf axils. Its creeping stems root readily at the nodes, allowing it to rapidly spread and outcompete surrounding grasses in damp soils.