Diodia (or buttonweed) is a genus of flowering plants in the family Rubiaceae.

The genus is found from southern and eastern United States, South America, Central America, Mexico, the West Indies and tropical Africa.

[2][3] Many species of Diodia have been transferred to a closely related genus Diodella, and therefore the name buttonweed also applies to these species.

There are also many species of false buttonweeds in the related genus Spermacoce.

Abutilon theophrasti in the family Malvaceae is also known by the common name of buttonweed.