''Eupatorium macrocephalum'' Less. aka pompom weed, is a cosmopolitan perennial plant belonging to the family of Asteraceae and regarded as an invasive weed in some countries. It is native to the southern United States, Central America, South America and was introduced to South Africa. It is classed as a principal weed in Brazil. In South Africa it has been cultivated as an ornamental, is often found on roadsides, and has become of concern for its invading of undisturbed climax grassland and wetlands since the 1960s. It is closely related to Siam weed, and is one of some 268 species in the genus.