Ageratina adenophora (synonym Eupatorium adenophorum), commonly known as Crofton weed, is a species of flowering plant in the family Asteraceae native to Mexico and Central America.

The small compound flowers occur in late spring and summer, and are found in clusters at the end of branches.

It was first inadvertently introduced to Yunnan around 1940, and its rapid spread is due in part to its allelopathic competition with other plant species.

[3] This species is host to the following insect induced gall: external link to gallformers Crofton weed is toxic to livestock.

[11] Ageratina is derived from Greek meaning 'un-aging', in reference to the flowers keeping their color for a long time.