Ageratum houstonianum Mill.

Erect or ascending annual herb, up to c. 1 m tall. Stems densely clothed in long eglandular and short glandular hairs above, becoming almost glabrous and sometimes somewhat woody toward base. Petiole hairy and glandular, 5–20–(50) mm long; lamina hairy and glandular especially on lower surface, ovate to ovate-triangular, acute, truncate to cordate, crenate-serrate, (12)–25–60–(100) × (12)–15–50–(70) mm; uppermost lvs smaller, sometimes with few teeth. Capitula c. 3–7 mm diam., in dense clusters; peduncles hairy and glandular. Involucral bracts ± equal, sometimes with supplementary bracts outside, oblong-triangular to lanceolate, acuminate, hairy and glandular, 4–5–(6) mm long. Florets usually blue and with conspicuous blue stigmas, rarely corolla and stigmas white. Achenes black, sparsely hairy, 1.4–1.8 mm long, with 5–(6), aristate, fimbriate scales.

[From: Webb et al. (1988) Flora of New Zealand. Volume 4.]

Flowering: Jan.–Dec.