Perennials or shrubs (sometimes scandent), 20–250 cm (fibrous-rooted). Stems erect or clambering, sparsely to densely branched. Leaves cauline; opposite [alternate, verticillate]; petiolate or sessile; blades usually 3-nerved from bases, mostly deltate to ovate or elliptic, sometimes linear, margins dentate or lobed, faces glabrous or puberulent to tomentose, sometimes gland-dotted. Heads discoid, in corymbiform to thyrsiform arrays. Involucres cylindric [campanulate to hemispheric], 2–7 mm diam. Phyllaries usually readily falling (at least in fruit), 18–65+ in 4–6+ series, 3–5-nerved, ovate to oblong or lanceolate, unequal (papery or herbaceous). Florets [6–]15–40[–75]; corollas white or purple to blue, lavender, or reddish, throats cylindric (lengths 3–4 times diams.); styles: bases not enlarged, glabrous, branches linear to linear-clavate. Receptacles flat to convex, paleate or epaleate. Cypselae prismatic, (3–)5-ribbed, scabrellous, usually gland-dotted as well; pappi persistent, of ca. 40 barbellate bristles in 1 series. x = 10.
se, sc United States, Mexico, Central America, South America (especially Brazil).
Species ca. 165 (4 in the flora).
|1||Leaves: petioles 0 or 0.5–1(–3) mm; blades linear-lanceolate to elliptic-lanceolate, bases tapered; apices of inner phyllaries ± spreading (pinkish purple, hyaline, petaloid, slightly expanded, truncate)||Chromolaena ivifolia|
|1||Leaves: petioles 5–20 mm; blades mostly deltate to ovate-lanceolate, bases ± abruptly contracted; apices of inner phyllaries appressed (not notably expanded or petaloid)||> 2|
|2||Shrubs; heads usually in 3s, sometimes borne singly; involucres turbinate to campanulate||Chromolaena bigelovii|
|2||Perennials or subshrubs; heads in clusters of 5–50+ in (terminal or lateral) corymbiform arrays; involucres cylindric||> 3|
|3||Leaf blades mostly 1.5–4 cm; involucres 5.5–7.5(–8) mm||Chromolaena frustrata|
|3||Leaf blades mostly (3.5–)5–10 cm; involucres (7–)8–10 mm||Chromolaena odorata|