Chromolaena gentianoides (Robinson) King & Robinson (1980b: 231)

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 : 160-163

2.5. Chromolaena gentianoides (Robinson) King & Robinson (1980b: 231) .

Brickellia gentianoides Robinson (1923: 42) . Eupatorium gentianoides (B.L.Rob.) Robinson (1932: 14) . Lectotype (designated by Christ & Ritter 2018: 112):— BRAZIL. Rio Grande do Sul, 1816–1821, A. Saint-Hilaire 768, Cat. C² 2739 (P! [P00707105])

= Eupatorium rhinanthaceum var. oinopolepis Malme (1933: 35) . Eupatorium oinopolepis (Malme) Cabrera (1963: 196) . Chromolaena oinopolepis (Malme) King & Robinson (1970c: 204) , syn. nov. Lectotype (designated by Christ & Ritter 2018: 112):— BRAZIL. Paraná: Curitiba, 16 March 1909, P. Dusén 8272 (S! [S-R-8980]). ( Fig. 11A–D , 12A–B )

Subshrubs, up to 1 m tall, decumbent, xylopodium present, branched from base or only in capitulescence; stems glabrous, non-glanduar, leafy until capitulescence. Leaves 4–4.3 × 0.5–07 cm, opposite, sessile, 3-veined, leaf blade elliptic, chartaceous, apex rounded to obtuse, base acute to attenuate, margins entire to serrate, adaxial surface glabrous, eglandular, abaxial surface glabrous, eglandular, margins eciliate. Primary capitulescence corymbose. Secondary capitulescence corymbose, axis glabrous, eglandular, bracteate, bracts 1.5–3.9 × 0.1–0.5 cm. Capitula pedunculate, peduncles 0.3–1.2 cm long, glabrous, eglandular, involucres campanulate, 6–6.4 × 4–4.2 mm, involucral bracts ca. 20, 4–5 series, outer deltate, 3–3.8 × 1.4–1.5 mm, apex acute, vinaceous, eciliate, glabrous, eglandular, erect to slightly recurved, abaxial surface vinaceous, 3-veined, glabrous, inner linear, 5.5–5.8 × 0.7–1 mm, apex acute, vinaceous, eciliate, glabrous, eglandular, erect, abaxial surface vinaceous, 1–3-veined, glabrous, receptacles epaleate. Florets 17–18, corollas 4.8–5.5 × 0.5–0.8 mm, lilac, lobes glabrous, eglandular. Cypselas obconical to oblong, 2.8–3.1 × 0.5–0.8 mm, 5–7-ribbed, ribs setuliferous, sinuses glabrous, eglandular, pappus setae ca. 35–50, stramineous, 5.1–5.5 mm long.

Distribution: — Brazil, in the states of Paraná, Rio Grande do Sul and Santa Catarina. In Rio Grande do Sul, it occurs in the physiographic region of Campos de Cima da Serra ( Fig. 13 , triangle).

Habitat: —Highland grasslands, usually in or close to wet soils, only in the Atlantic Forest.

Phenology: —Flowers from the end of summer to the beginning of autumn, with a flowering peak in March and April.

Etymology: —The specific epithet is a reference to the genus Gentiana L. ( Gentianaceae ), with which this species shows some morphological similarity.

Comments: — Chromolaena gentianoides is considered a neglected species. Since its original description, the species was cited from Rio Grande do Sul only by Barroso (1950), based solely in the type collection. It is also considered rare as there are only two records in the state: the original record by Saint-Hilaire and the specimen collected in this study, nearly 200 years after the original.

Chromolaena rhinanthacea is the most similar species to C. gentianoides , both of them sharing a number of common characters mostly referent to the vegetative parts, such as the indumentum of stems and leaves and the shape of leaves. However, they can be easily distinguished by the reproductive characters, specially the general characters of the involucres: C. gentianoides has involucral bracts always with acute apices and conspicuously vinaceous, a character not recorded in C. rhinanthacea . The former also has a greater number of florets than the latter. The general appearance of the involucre is somewhat abnormal in Chromolaena , particularly in the study area, making it a very useful character to identify this species.

Chromolaena oinopolepis is synonymized here for the first time under C. gentianoides . There is an evident morphological similarity between the type specimens of both species, and, while recombining B. gentianoides to E. gentianoides, Robinson (1932) indicated Dusén 14911 as one of the examined specimens. This specimen was actually identified by Malme (1933) as E. rhinanthaceum var. oinopolepis , the basionym of C. oinopolepis , and is cited by this author as one of the examined specimens under the description of this species. We consider this issue a further evidence that two species are, in fact, a single entity.

Specimen examined: — BRAZIL: Rio Grande do Sul: Jaquirana: Parque Estadual do Tainhas, 03 March 2018, Christ A.L. 501 (ICN).

Figures

FIGURE 11A–D: Chromolaena gentianoides. A. Fertile specimen. B. Capitulum. C. Involucral bracts. D. Floret. E–I: Chromolaena hirsuta. E. Fertile specimen. F. Capitulum. G. Involucral bracts. H. Floret. I. Palea.

FIGURE 12A–B: Chromolaena gentianoides. A. Primary capitulescence. B. Leaves. C–E: Chromolaena hirsuta. C. Primary capitulescences. D. Xylopodium. E. Leaves. Credits: Anderson Christ (A–B, D) and Sérgio Bordignon (C, E).

FIGURE 13: Distribution of C. gentianoides (triangle) and C. hirsuta (circles) in Rio Grande do Sul.