Chromolaena christieana (Baker) King & Robinson (1970c: 200)

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 : 153-154

2.2. Chromolaena christieana (Baker) King & Robinson (1970c: 200) . Eupatorium christieanum Baker (1876: 298) .

Type:— BRAZIL. Paraná, 1858, W.D. Christie s.n. (holotype K! [ K 0004868884).

= Eupatorium laevigatulum Robinson (1926: 21) . Type:— PARAGUAY. s.l., March 1913, E. Hassler 11584 (holotype GH! [GH00007748], isotypes C, G) ( Fig. 5F–J , 6D–F ).

Subshrubs, up to 1.5 m tall, erect, xylopodium absent, branched from base or only in capitulescence; stems glabrous to glabrescent, eglandular, leafy until capitulescence. Leaves 3.3–9.2 × 0.4–1.7 cm, opposite, petiolate, 3-veined, leaf blade lanceolate to linear-lanceolate, membranaceous, apex acute to attenuate, base acute to attenuate, margins sparsely serrate, sometimes entire, adaxial surface glabrous, eglandular, abaxial surface glabrous, eglandular, margins eciliate, petioles 0.3–1.6 cm long, glabrous, eglandular. Primary capitulescences corymbose. Secondary capitulescences corymbose, axis glabrous to puberulous, eglandular, bracteate, bracts 1.7–4.8 × 0.2–1.4 cm, petioles 0.2–0.3 cm long, glabrous, eglandular. Capitula subsessile to pedunculate, peduncles 0.2–1.8 cm long, puberulous, eglandular, involucres cylindrical, 5.7–7.6 × 2–3.2 mm, involucral bracts 18–22, 4–5-seriate, outer ovate, 1–3.3 × 0.9–1.5 mm, apex acute, citrine, eciliate, glabrous, eglandular, appressed, abaxial surface white to citrine, 3–5-veined, glabrous, inner linear, 5–7 × 0.8–1.2 mm, apex acute to rounded, citrine to pink, non-petaloid, eciliate, glabrous, eglandular, appressed, abaxial surface white to citrine, 3–5-veined, glabrous, receptacles epaleate. Florets 5–13, corollas 3.6–5.2 × 0.5–0.8 mm, lilac or rarely white, lobes glabrous, eglandular. Cypselas obconical, 2.7–3.8 × 0.5–0.7 mm, 3–5-ribbed, ribs and sinuses glabrous to setuliferous, eglandular, pappus setae ca. 27–33, stramineous, 3.8–5 mm long.

Distribution: — Argentina , Paraguay ( Freire & Ariza Espinar 2014b) and Brazil. In Brazil, it occurs in Goiás, Mato Grosso do Sul, Mato Grosso, Paraná and Rio Grande do Sul. In Rio Grande do Sul, it is recorded only in the Espinilho State Park, municipality of Barra do Quaraí, physiographic region of Campanha ( Fig. 7 , circle).

Habitat: —Grasslands with occurrence of Vachellia caven (Molina) Seigler & Ebinger ( Fabaceae ) (vernacular name “espinilho”) in the Pampa biome.

Phenology: —Flowers mainly during summer, with a flowering peak in February and March.

Etymology: —The specific epithet is a homage to William Dougal Christie, collector of the type specimen of this species.

Comments: — Chromolaena christieana is one of the rarest species of Chromolaena found in Rio Grande do Sul, where it is known in a single locality in the westernmost municipality of the state, near the border with Uruguay and Argentina . The species is far more common in neighboring countries such as Argentina and in other Brazilian states, mainly in Mato Grosso do Sul. The species wasn’t recorded by Matzenbacher (1979), but was later included in the expansion of the original key of this study ( Matzenbacher & Schneider 2008).

This species is somewhat similar to C. laevigata , also a subshrub or shrub with mostly glabrous leaves and stems. The two species can be distinguished by the fewer florets in the capitula, the narrower, more membranaceous leaves and the puberulous indumentum of the peduncles of C. christieana . This species is also very similar to C. margaritensis (Hassl.) R.M.King & H. Rob. , a species that does not occur in Rio Grande do Sul but co-occurs with C. christieana in Paraguay and in Mato Grosso do Sul, Brazil. They can be differentiated by the tomentose indumentum of the stems, leaves and involucral bracts of C. margaritensis .

Specimens examined: — BRAZIL: Rio Grande do Sul: Barra do Quaraí: Parque Estadual do Espinilho , February 1990, Sobral, M. & Falkenberg, D. B. 6351 ( ICN, UEC, FLOR) ; 01 December 2016, Christ, A. L. 334 ( ICN) .

Figures

FIGURE 5A–E: Chromolaena callilepis. A. Fertile branch. B. Capitulum. C. Involucral bracts. D. Floret. E. Palea. F–J: Chromolaena christieana. F. Fertile branch. G. Capitulum. H. Involucral bracts. I. Floret. J. Peduncle.

FIGURE 6A–C: Chromolaena callilepis. A. Primary capitulescence. B. Leaves. C. Capitula. D–F: Chromolaena christieana. D. General view. E. Primary capitulescence. F. Leaves. Credits:Angelo Schneider (A) and Anderson Christ (B–F).

FIGURE 7: Distribution of C. callilepis (triangles) and C. christieana (circle) in Rio Grande do Sul.