Chromolaena Candolle (1836: 133)

Christ, Anderson Luiz & Ritter, Mara Rejane, 2019, A taxonomic study of Praxelinae (Asteraceae-Eupatorieae) in Rio Grande do Sul, Brazil, Phytotaxa 393 (2), pp. 141-197 : 149-150

2. Chromolaena Candolle (1836: 133) . Eupatorium sect. Chromolaena (DC.) Bentham ex Baker (1876: 300) .

Type:— Chromolaena horminoides DC.

= Eupatorium sect. Cylindrocephalum Candolle (1836: 141) . Lectotype (designated by King & Robinson 1975: 923):— Eupatorium odoratum Linnaeus (= Chromolaena odorata (L.) R.M.King & H.Rob.).

= Osmia Schultz-Bipontinus (1866: 251) . Eupatorium sect. Osmia (Sch.Bip.) Bentham ex Baker (1876: 275) . Type:— Eupatorium odoratum Linnaeus (= Chromolaena odorata (L.) R.M.King & H.Rob.).

Subshrubs or shrubs, erect, decumbent or rarely reclining, xylopodia present or not, branched from base, along stem or only in capitulescence; stems sulcate, glabrous to villose, glandular or eglandular, leafy until capitulescence or only in lower half, then aphyllous or near-aphyllous in upper half. Leaves opposite or alternate, petiolate or sessile, 1–3- veined, membranaceous to coriaceous, adaxial surface glabrous to hirsute, sometimes strigose only on veins, eglandular to sometimes glandular, abaxial surface glabrous to villose, sometimes strigose to hirsute only on veins, glandular or eglandular; margins ciliate or eciliate; petioles glabrous to villose, glandular or eglandular. Primary capitulescences corymbose, glomeruliform or dichasia. Secondary capitulescences corymbose, paniculate, umbel-like, candelabra-shaped or compound dichasia, axis sulcate, glabrous to villose, glandular or eglandular, bracteate or ebracteate, bracts similar to leaves, petioles glabrous to villose, glandular or eglandular. Capitula sessile to long pedunculate, peduncles glabrous to tomentose, glandular or eglandular, involucres imbricate, cylindrical to campanulate, involucral bracts 14–50, 4–8-seriate, persistent, outer ovate to oblong, sometimes deltate or elliptic, apex acuminate to truncate, stramineous to vinaceous, ciliate or eciliate, glabrous to tomentose, glandular or eglandular, appressed to squarrose, abaxial surface white to vinaceous, 3–6-veined, glabrous to puberulous, inner linear to spatulate, apex acuminate to rounded, stramineous to vinaceous, petaloid or not, ciliate or eciliate, glabrous to tomentose, glandular or eglandular, appressed to squarrose, abaxial surface white to vinaceous, 1–5-veined, glabrous to tomentose, receptacles flat, epaleate or paleate; paleae 0–7, linear to acicular, 1–3-veined, apex stramineous to pink, abaxial surface white to stramineous, ciliate or eciliate, glandular or eglandular. Florets 5–60, corollas tubular, lilac or white, lobes glabrous to puberulous, glandular or eglandular. Cypselas obconical to oblong, 3–8-ribbed; ribs and sinuses glabrous to setuliferous, glandular or eglandular, carpopodia symmetric, pappus setae ca. 23–47, white to stramineous.

Distribution: —Genus native to the American continent, occurring from southern United States to northern Argentina , with one adventive weedy species in Asia, Africa and some Pacific isles ( King & Robinson 1987). In Brazil, there are records of 69 species throughout the entire territory, occurring in all biomes ( Flora do Brasil 2020 in development, 2018). In Rio Grande do Sul, Chromolaena can be found in all physiographic regions.

Habitat: —Mostly in grasslands, sometimes in forest edges. Some species are typical of anthropogenic environments. Occurs in both Atlantic Forest and Pampa.

Phenology: —Fertile specimens were collected mostly from the end of spring to the beginning ot autumn, with a flowering peak from January to April.

Etymology: —Greek chromos (colorful) and laena (involucre), with reference to the involucral bracts usually bearing showy colors, at least at the apices.

Comments: — Chromolaena is the second largest genera originated from the segregation of Eupatorium , comprising ca. 166 species ( Freire & Ariza Espinar 2014b); the largest is Ageratina Spach , which does not occur in Brazil ( Esteves 2001). The genus is also the second largest of the tribe to occur in Brazil after Mikania Willd. , and is most diverse in the Midwestern and Southeastern regions, especially in the Cerrado biome ( Flora do Brasil 2020 in development, 2018).

Species of Chromolaena are common in Rio Grande do Sul, occurring through the entire territory of the State. They are usually most common in grasslands of the Atlantic Forest biome, in the northern half of the State, but the genus can also be frequently found in transition sites between the Atlantic Forest and the Pampa. Chromolaena can be easily recognized by the usually cylindrical capitula, and the numerous involucral bracts more than 4-seriate, all of them deciduous, but not caducous. The florets are usually lilac and the involucral bracts usually bear showy colors, mostly pink or vinaceous, which helps in the recognition of the genus.

The following 17 species of Chromolaena are native to Rio Grande do Sul: