Creeping croftonweed

Ageratina riparia, the creeping croftonweed or mistflower, is a low-growing, sprawling perennial herb of the Asteraceae family that may reach up to one metre in height. Its stems are somewhat woody at the base, covered with purple-tinged hairs, and produce additional adventitious roots wherever they touch moist ground, allowing the plant to spread vegetatively. Leaves are opposite, lance-shaped to narrowly ovate, averaging about 7.5 cm long and 2.5 cm wide, with serrated margins and a tapered tip and base. Dense, flat-topped clusters of small white flower heads appear at the branch tips, blooming from late winter into autumn in mild climates. Each plant can produce between ten thousand and a hundred thousand slender, black, wind- and water-dispersed seeds, and the species is a significant invasive weed in Hawaii, southern Africa, Southeast Asia and Oceania, where it forms dense mats in damp pastures, stream banks and forest margins. The plant is native to western Mexico.