Diodia is a genus of flowering plants in the coffee family, Rubiaceae, in the order Gentianales. It was described by Carl Linnaeus in 1753 in Species Plantarum. Commonly known as buttonweeds, the genus comprises roughly two dozen species (GBIF's backbone taxonomy lists 23 accepted taxa) of herbaceous plants distributed across warmer regions of the Americas and Africa. Its range spans the southern and eastern United States, South America, Central America, Mexico, and the West Indies, along with tropical Africa.
The taxonomic boundaries of the genus have shifted over time: many species once placed in Diodia have since been transferred to the closely related genus Diodella, so the common name "buttonweed" is also applied to those segregate species. The name is also used for several species of the related genus Spermacoce ("false buttonweeds") and, unrelatedly, for Abutilon theophrasti in the mallow family (Malvaceae), which shares the common name despite no close relationship.
The best-known member is Diodia virginiana (Virginia buttonweed), a low, spreading herb native to the south-central and south-eastern United States — from Texas to Kansas, east to Florida and New Jersey, plus Connecticut — and also found in Cuba and Nicaragua; it has become naturalized as a lawn weed in Japan, Taiwan, and northern California. Other species illustrate the genus's broad distribution, such as D. kuntzei (Venezuela, Bolivia, Peru, Brazil, Argentina, Paraguay) and D. verticillata (Brazil and the Lesser Antilles) in the Neotropics.
Distribution
Diodia occurs from the southern and eastern United States through South America, Central America, Mexico, and the West Indies, with additional species in tropical Africa. GBIF's backbone taxonomy places the genus in family Rubiaceae, order Gentianales.
Taxonomy Notes
Many species formerly classified in Diodia have since been moved to the segregate genus Diodella, which shares the common name "buttonweed." The name is also loosely applied to related "false buttonweeds" in the genus Spermacoce and, unrelatedly, to Abutilon theophrasti (family Malvaceae).
