Chromolaena

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.

Distribution

se, sc United States, Mexico, Central America, South America (especially Brazil).

Discussion

Species ca. 165 (4 in the flora).

Selected References

None.

Lower Taxa

Chromolaena bigelovii, Chromolaena frustrata, Chromolaena ivifolia, Chromolaena odorata

Key

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