Diodia virginiana is a plant species in the Rubiaceae, and its common name is Virginia buttonweed. It is a spreading, matted perennial with opposite leaves, often mottled by a virus that attacks the foliage.

The flowers are white, cross-shaped, and have four petals. The fruit is green and often floating on water. The species can become a nuisance weed, hard to eradicate because underground parts remain behind when you try to pull the plant.

It occurs in many habitats, including moist to wet areas and areas subject to periodic inundation, like temporary ponds and the savannas in the upper Florida panhandle. This spreading, matted perennial is often mottled due to a virus yet still produces white, cross-shaped flowers and floating fruits​.

Source: Wikipedia.