Ageratina riparia (Regel) R.M.King & H.Rob.

Herb or subshrub, 0.3–1 m high; stems erect or sprawling, spreading-prostrate in lower parts, rooting at nodes, purplish, sparsely to densely pubescent, not glandular. Leaves with petioles to 15 mm long; lamina lanceolate to narrowly lanceolate, narrowly ovate or narrowly elliptic, 30–120 mm long, 8–30 mm wide, cuneate-attenuate at base, coarsely serrate, glabrescent to sparsely short-pilose, especially on abaxial veins, slightly discolorous. Capitula 3–6 mm diam., numerous, grouped in terminal and sometimes axillary loose corymbs; involucral bracts in 2 series, narrowly lanceolate, 3–4 mm long, puberulent, sparsely short-pilose, not glandular, 1-or 2-veined. Corollas 3–5 mm long. Achenes 1.5–2 mm long, 5-ribbed, setulose on ribs, black. Pappus bristles c. 10, 3–4 mm long, scabrid. [See also Green (1994: 403).]

A serious weed in native ecosystems and a minor problem in agricultural land: a declared noxious weed in parts of New South Wales and Queensland. Found in damp sites in a wide range of communities, from rainforest margins, vine thickets, dry or wet Eucalyptus woodland, along creek banks (and even in shallow water), in coastal shrubberies and in grassy pastures, from near sea level to 1210 m altitude. On Norfolk Island a serious weed in areas of degraded forest, and an invader of the margins of undisturbed forest, smothering ferns and seedlings (Green 1994: 403).

Can be grown by seedlings.