Conyza is a genus of flowering plants in the daisy family, Asteraceae (order Asterales), formally described by John Hill in 1756. Common names for members of the genus include horseweed, butterweed, and fleabane. Species in the genus are annual or perennial herbaceous plants, rarely shrubs, typically growing 1–2 m tall, with erect, branched stems bearing alternate leaves. The small flower heads are produced in inflorescences, with several inflorescences loosely clustered on each stem, a typical arrangement within Asteraceae.
The genus is native to tropical and warm temperate regions across the world, with some species extending north into cool temperate zones in North America and eastern Asia. Its New World species are closely related to the genus Erigeron (also commonly called fleabane), and taxonomic treatments have historically shifted species back and forth between the two genera.
Many Conyza species behave as ruderal plants, readily colonizing disturbed ground, roadsides, and agricultural land. This weedy habit has practical significance in agriculture: several species have developed resistance to the widely used herbicide glyphosate, making them persistent weeds in cropping systems in various parts of the world.
Distribution
Conyza species are native to tropical and warm temperate regions worldwide, with some extending into cool temperate areas of North America and eastern Asia. GBIF confirms placement in family Asteraceae, order Asterales.
Ecology
Many Conyza species are ruderal, colonizing disturbed habitats, and several have evolved resistance to the herbicide glyphosate, making them problematic agricultural weeds.
Taxonomy Notes
Conyza was described by John Hill in 1756 (published in Brit. Herb.) and is accepted in GBIF's backbone taxonomy within Asteraceae/Asterales. New World Conyza species are closely related to Erigeron, and the boundary between the two genera has shifted in different taxonomic treatments.
