Praxelis Cassini (1826: 261)

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 : 144-145

1. Praxelis Cassini (1826: 261) . Eupatorium sect. Praxelis (Cass.) Bentham ex Baker (1876: 341) .

Type:— Praxelis villosa Cassini (= Praxelis diffusa (Richard) Pruski ).

= Ooclinium Candolle (1836: 133) . Lectotype (designated by King & Robinson 1969: 338):— Ooclinium grandiflorum Candolle (= Praxelis grandiflora (DC.) Schultz-Bipontinus ).

Herbs or subshrubs, rarely shrubs, erect or decumbent, xylopodia absent, branched from base or only in capitulescence; stems sulcate, hirsute, rarely glabrous to glabrescent, eglandular, leafy until capitulescence. Leaves opposite, petiolate or sessile, 3-veined, papyraceous to chartaceous, adaxial surface glabrescent to hirsute, rarely glabrous, eglandular, abaxial surface strigose to hirsute, glandular or eglandular, margins ciliate, petioles hirsute, eglandular. Primary capitulescences corymbose or umbellate, sometimes capitula solitary. Secondary capitulescences paniculate, axis sulcate, hirsute, eglandular, bracteate or ebracteate, bracts similar to leaves, petioles hirsute, eglandular. Capitula sessile to long pedunculate; peduncles strigose to hirsute, eglandular; involucres subimbricate, campanulate; involucral bracts 17–25, 2–3-seriate, caducous, outer deltate to lanceolate, apex acute to caudate, citrine to pink, eciliate, glabrous to hirsute, eglandular, erect to recurved, abaxial surface stramineous to citrine, 3–7-veined, glabrous to hirsute, inner linear to spatulate, apex attenuate to truncate, sometimes acuminate, citrine to pink, non-petaloid, eciliate, glabrous to puberulous, eglandular, erect to recurved, abaxial surface stramineous to citrine, 3–7-veined, glabrous; receptacles conical, epaleate. Florets 32–95; corollas tubular, lilac or white, lobes glabrous to puberulous, glandular or eglandular. Cypselas obconical or rarely biconvex, black, 2–4-ribbed; ribs and sinuses setuliferous to rarely glabrous, eglandular; carpopodia asymmetrical; pappus setae ca. 13–31, white to ferruginous.

Distribution: —Genus endemic to South America, occurring in Argentina , Bolivia, Brazil, Colombia, French Guiana, Guiana, Paraguay, Peru and Venezuela ( King & Robinson 1987). Two species are invasive in Australia, Hong Kong, North American and Taiwan ( Teles et al. 2016). Sixteen species are recorded in Brazil, occurring throughout the territory and in all biomes ( Flora do Brasil 2020 in development, 2018). In Rio Grande do Sul, Praxelis occurs only in the physiographic regions of Alto Uruguai, Campanha, Depressão Central, Litoral and Missões.

Habitat: —Grasslands with shallow and rocky soils or in anthropogenic environments such as roadsides and wastelands. Occurs in both Atlantic Forest and Pampa.

Phenology: —Fertile specimens have been collected throughout the year, with a flowering peak from December to March.

Etymology: —The etymology of Praxelis wasn’t explained by its author in the protologue, and no further references explaining its meaning were found.

Comments: —Despite being the type of the subtribe, Praxelis is only its second largest genus, after Chromolaena . According to King & Robinson (1987), there are 16 species exclusive to South America. Abreu (2015), in an unplubished thesis, however, reported the occurrence of 17 species in Brazil. Teles et al. (2016) described a new species and proposed a new combination in Praxelis , indicating that further studies are necessary to better clarify the total number of species in this genus. Most species native to Brazil occur in the Midwestern or Southeastern regions, mostly in the Cerrado biome.

The two species of Praxelis found in Rio Grande do Sul have a number of morphological differences between them, and are quite easy to recognize. They also show completely different habitat preferences: P. clematidea is ruderal, typical of anthropogenic environments, while P. missionum is exclusive of shallow soils, usually occurring in or near rocky outcrops.

Besides Praxelis , the only other genus of Praxelinae occurring in Rio Grande do Sul is Chromolaena . Both genera can be differentiated through the type of involucres (subimbricate in Praxelis and imbricate in Chromolaena ); the number of series of involucral bracts (2–3 in the former and more than 4 in the latter); the shape of the receptacles (conical in the former and flat in the latter); and through the symmetry of the carpopodia (asymmetric in the former and symmetric in the latter). Furthermore, the involucral bracts in Chromolaena are only deciduous, never caducous, as in the native species of Praxelis . Some of these features, however, are applicable only to the species native to Rio Grande do Sul, since other species of Praxelis may possess imbricate involucres and persistent involucral bracts.

In Rio Grande do Sul, the following two species of Praxelis are found: