Ageratum houstonianum Mill. APNI*
Description: Erect or decumbent branched herb, 0.3–1 m high, coarsely hairy or nearly glabrous.
Leaves ovate to triangular, 2–7 cm long, 1.5–6 cm wide, apex acute to obtuse, margins regularly toothed, both surfaces with scattered hairs; petiole 5–30 mm long, hairy.
Corymbs compact; corymb branches 3–8 mm long, ± coarsely hairy; heads ± globose, 6–8 mm diam.; involucral bracts linear-lanceolate, c. 5 mm long, coarsely hairy. Florets blue-mauve.
Achenes c. 2 mm long, black, glabrous or sparsely hairy; pappus of c. 5 white awned scales, 2–3 mm long.
Flowering: most of year, mainly summer.
Distribution and occurrence: Common weed of wasteland; north from Sydney district. Native of Mexico, widespread in C Amer.
NSW subdivisions: *NC, *CC, *SC
Other Australian states: *Qld
Text by M. F. Porteners
Taxon concept: Flora of NSW 3 (1992)
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