[Wikipedia] Origins and Introduction: 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. Originally grown as an ornamental plant, it has become invasive into farmland and bushland worldwide. It is toxic to horses, who develop a respiratory disease known as Numinbah Horse Sickness after eating it. (link added by Jessica Johnston)