Richardia is a genus of approximately fifteen species of flowering plants in the family Rubiaceae, within the order Gentianales. Commonly known as Mexican-clover, the genus consists mostly of annual herbs, with a few herbaceous perennial species. Plants in this genus are typically low-growing and produce small, tubular flowers in dense terminal heads.
The genus is native to tropical and warm-temperate regions of the Americas, ranging from the southeastern United States and Mexico through Central America and the Caribbean to South America as far south as northern Argentina. One species, Richardia brasiliensis, has also naturalized or is native beyond the Americas, extending to Fiji. Several species, including Richardia scabra and Richardia brasiliensis, are considered weedy and have spread widely beyond their native ranges, becoming invasive in parts of Africa, Asia, and elsewhere.
A nomenclatural note: Richardia Kunth (non L.) is a separate, now-synonymized name that was once applied to the genus Zantedeschia (calla lilies) in the family Araceae. The two genera are unrelated; the plant genus formally known as Richardia belongs strictly to Rubiaceae.
Distribution
Richardia is native to tropical and warm-temperate regions of the Americas, from the southeastern United States south through Mexico, Central America, and South America to northern Argentina. One species is also recorded from Fiji. Several species have become naturalized weeds across tropical regions worldwide.
Taxonomy Notes
The name Richardia Kunth non L. — once applied to the genus now known as Zantedeschia (calla lilies, family Araceae) — is a nomenclatural synonym unrelated to the Rubiaceae genus. The valid genus Richardia belongs to the family Rubiaceae, order Gentianales. Within Rubiaceae it is placed in the tribe Spermacoceae.
