Ageratum houstonianum

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.