Tridax is a genus of flowering plants in the family Asteraceae (the daisy family), placed in the order Asterales. The genus is native primarily to the tropical regions of North and South America, with its center of diversity in Mexico and Central America. Plants in this genus are herbaceous, typically producing composite flower heads characteristic of the Asteraceae family, with ray florets surrounding a central disc.
The genus is perhaps best known through its most widespread member, Tridax procumbens (coatbuttons or tridax daisy), a sprawling annual or perennial herb that has spread far beyond its native range and become naturalized across the southern United States, tropical Africa, Asia, and Australia, where it is regarded as a noxious weed in agricultural and disturbed habitats.
Tridax belongs to a diverse family that includes sunflowers, daisies, and chrysanthemums. The genus has undergone taxonomic revision; several species formerly placed in Tridax have been transferred to related genera including Calea, Layia, and Sabazia.
Distribution
Tridax is native primarily to the tropical regions of North and South America. The most widespread species, Tridax procumbens, has become naturalized in the southern United States, tropical Africa, Asia, and Australia, and is considered a noxious weed in many of those regions.
Taxonomy Notes
Several species formerly placed in Tridax have been transferred to other genera: Tridax accedens and Tridax verticillata are now Calea verticillata; Tridax ehrenbergii is now Sabazia sarmentosa; and Tridax gaillardioides is now Layia gaillardioides. GBIF currently recognizes a small number of accepted species within the genus.
