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Ageratina adenophora (Sprengel) R. King & H. Robinson
(=Eupatorium adenophorum Sprengel)
Family: Asteraceae, Tribe: Eupatorieae
Common names: crofton weed
Fruit an achene, narrowly elliptic to narrowly oblanceolate, often gibbous, 1.5-2 mm long, 0.3-0.5 mm in diameter; with 5 prominent ribs, cross section 5 sided, sides +/- concave. Surface glistening, dark brown to black. Scar basal, a short, light brown, cylindrical collar. Pappus one row of 5-10 +/- flexible white plumose bristles, 2.5-4 mm long. Pappus easily deciduous, often absent. Style base straw-colored, +/- cylindrical, closed, usually flanged, surrounded by honey-brown ring. Apical collar conspicuous (more so if pappus absent), straw colored, horizontal, round, +/- flanged or rounded. Embryo linear; endosperm absent.
Ageratina riparia (Regel) R. King & Robinson (=Eupatorium riparium Regel)
Mikania scandens (L.) Willd.
Mikania micrantha Kunth
Mikania cordata (Burm. f.) Robinson
Africa: Zimbabwe; Asia: India, Philippines, Thailand; Europe: France, Greece, Portugal, Spain; Oceania: Australia, New Guinea, New Zealand, Tasmania; North America: Mexico, Trinidad and Tobago, United States.
Native to Mexico.
Humid subtropics, primarily in creek beds and forest clearings; coastal areas, roadsides, overgrazed pastures.
Ageratina adenophora is a perennial herb, up to 2 m tall. It was introduced to Hawaii and Australia as an ornamental, but has now become naturalized, invading pastures, reducing the carrying capacity of grazing lands, and restricting movement of animals and machines. Cattle find it unpalatable, and horses are poisoned by it. The plant spreads primarily by seed; its achenes are dispersed by wind and water, and in mud sticking to animals and equipment. Light is required for germination, so A. adenophora does not invade dense, well managed pastures.