Ageratum (meksikonsinitähtönen) – Ageratum houstonianum

Stems are erect, simple or branched from middle or lower part, softly hairy (pubescent). Leaves are often opposite, and may be alternate in upper parts of the stem. Blades are broadly ovate or triangular-ovate, basally 3-veined or inconspicuously 5-veined, both surfaces sparsely or densely white pubescent, base cordate or truncate, margin crenate-serrate, apex rounded or acute. Petiole is 0.7-3 cm. The flower-heads (capitula) are arranged in dense 2-4 cm clusters at the tips of the branches (in terminal corymbs), and do not have any obvious 'petals' (rayflorets). Each flower-head (5-8 mm across) has numerous tiny tubular florets that are surrounded by two or three rows of greenish-coloured bracts (an involucre). Bracts are narrowly lanceolate, 4-5 mm, long acuminate and covered in sticky hairs (glandular pubescent). Corollas are tubular, 2.5-3.5 mm long, pale lavender to blue, pink or purplish, each with two elongated projections (style branches). Peduncles are densely pubescent. Fruit is a brown to black achene, 5-angled, ca. 2 mm long, topped with five whitish awn-tipped scales (i.e. pappus).