Conyza (horseweed, butterweed or fleabane) is a genus of about 50 species of flowering plants in the family Asteraceae, native to tropical and warm temperate regions throughout the world, and also north into cool temperate regions in North America and eastern Asia. The genus is closely related to Erigeron (also known as fleabanes).
The species are annual or perennial herbaceous plants, rarely shrubs, growing to 1-2 m tall. The stems are erect, branched, with alternate leaves. The flowers are produced in inflorescences, with several inflorescences loosely clustered on each stem.
The species has been found to be resistant to the Monsanto herbicide Roundup, in some cases.Selected species