Chromolaena nervosa (Chodat) A.L.Christ

Christ, Anderson Luiz, Nakajima, Jimi Naoki & Ritter, Mara Rejane, 2025, Towards a better understanding of the Chromolaena congesta complex (Asteraceae, Eupatorieae): updated synopsis with taxonomic novelties, Phytotaxa 689 (2), pp. 163-184 : 176-178

9. Chromolaena nervosa (Chodat) A.L.Christ , comb. & stat. nov. Eupatorium caaguazuense var. nervosum Chodat (1902: 306) . Type:— PARAGUAY. Carimbatay, Sep. 1898 –1899, E. Hassler 4567 (lectotype: G00381829!, step I designated by Freire & Ariza Espinar

(2014: 339), step II designated here; isolectotypes: BM000096329 !, G00381859 !, G00381849 !, G00381848 !, GH00007574 !). ( Fig. 5A–F )

Description: — Subshrubs up to 50 cm tall, erect or decumbent, xylopodium present, branched only in capitulescence. Stems hirsute to villose, rarely puberulous, mostly eglandular, rarely glandular, leafy until capitulescence, internodes 0.5–11.2 cm long. Leaves 2.1–5 × 1.4–2.7 cm, opposite, petiolate, 3–5-veined, veins emergent on abaxial surface, leaf blade ovate, rarely lanceolate or deltade, coriaceous, concolor, apex acute to obtuse, rarely rounded, base truncate to rounded, rarely cuneate or cordate, margins crenate, adaxial surface strigose to hirsute, eglandular, abaxial surface strigose to villose, glandular, petioles 1.7–5 mm long, hirsute to villose, eglandular. Primary capitulescence glomerate to corymbose. Secondary capitulescence antellate, branches puberulous to villose, eglandular, bracteate, bracts similar to ordinary leaves. Capitula sessile to subsessile, peduncles up to 0.3 cm long, puberulous to tomentose, glandular, involucres cylindrical to campanulate, 5.6–7.8 × 2.4–3.5 mm, involucral bracts 13–25, 4–5-seriate, outer oblong to ovate, 2.4–3.6 × 0.9–1.9 mm, apex cuneate, citrine to vinaceous, ciliate, puberulous, mostly glandular, very rarely eglandular, mostly recurved, sometimes erect, abaxial surface citrine, 3-veined, glabrous to puberulous, inner linear, 5.4–6.6 × 0.7–1.5 mm, apex acuminate, rarely acute, vinaceous, ciliate, puberulous, mostly glandular, rarely eglandular, recurved to erect, abaxial surface citrine to vinaceous, 1–3-veined, glabrous to puberulous, receptacles epaleate. Florets 8–13, corollas 4.1–5.4 × 0.6–1 mm, lilac, lobes glabrous to puberulous, glandular. Cypselae obconical, 2.4–3.1 × 0.4– 0.8 mm, 5–7-ribbed, glabrescent to setulliferous, eglandular, pappus setae ca. 32–40, stramineous, 4.3–5.2 mm long.

Distribution: — Argentina (Corrientes and Misiones provinces), Brazil (Mato Grosso do Sul, Paraná, Rio Grande do Sul and São Paulo states) and Paraguay (Alto Paraná, Amambay, Caaguazú, Caazapá, Cordillera, Misiones and San Pedro departments). Chromolaena nervosa is typical of dry grasslands from the Río de la Plata grasslands.

Flowering period: —Flowers mostly from January to April.

Conservation status: —Near Threatened (NT). Despite the inferred AOO of this species suggesting a status of Endangered, there are more than five known populations of C. nervosa throughout its range, and these are usually composed of multiple mature individuals. Despite that, this species is not known to be protected in any conservation units. Furthermore, many populations occur near anthropized sites such as roadsides or wastelands, and many grasslands in the Río de la Plata region are known to be under pressure of conversion for usage as agricultural lots or pastures ( Yezzi et al. 2021), suggesting this species could be at risk of losing suitable habitats soon. Still, continued observations and accompaniment of its populations are needed to clarify if that would be that case and what measures can be done to aid in the conservation of C. nervosa .

Comments: — Chromolaena nervosa is here treated for the first time as species, since many authors have previously treated it as a synonym of C. squarrulosa (e.g. Cabrera et al. 1996, Freire & Ariza Espinar 2014, Christ & Ritter 2019) ( Table 1) or simply ignored it in their treatments of Chromolaena and Eupatorieae (e.g. Esteves 2001). This species can be recognized mostly by the hirsute or villose indument of stems, branches and leaves ( Fig. 5B–C, E–F ); venation emergent on the abaxial surface of the leaves ( Fig. 5F ); leaves usually patent or pendant ( Fig. 5B, E–F ); antellate secondary capitulescence; and cypselae lacking glandular hairs. Chromolaena nervosa is like C. elliptica , both possessing cuneate outer phyllaries and tendency of having leaves twice as long as wide. It differs from this species mostly through the indument of the stems, branches and leaves (usually strigose or puberulous in C. elliptica ), absence of glandular hairs from the cypselae (vs. cypselae glandular) and leaves ovate, with truncated to rounded bases (vs. leaves elliptic, with cuneate bases).

We also provide a second step lectotypification for E. caaguazuense var. nervosum . A lectotype was previously indicated by Freire & Ariza Espinar (2014) as being deposited in G, but without any specification on which specimen. However, when searching for it, we found out that there are four specimens bearing labels befitting the protologue of E. caaguazuense var. nervosum ; any of them could be understood as the specimen selected by Freire & Ariza Espinar (2014). To solve this, we elected specimen G00381859 as the lectotype, while the remaining specimens are treated as isolectotypes. The specimen we chose was considered as the most similar to the morphological description of this taxon, while also showing the known variation in leaf shape and size observed in populations.

Selected specimens: — ARGENTINA. Corrientes, Santo Tomé, 23 March 1977, A. L. Cabrera 28292 ( SI). Misiones: Loreto , 27 March 1910, Rodriguez 246 ( LP) . BRAZIL. Mato Grosso do Sul: Ponta Porã, Fazenda Itamarati, 20 March 1985, G. Hatschbach 49328 ( MBM). Paraná: Arapoti , 24°06’00.0”S, 49°22’00.0”W, 17 January 1965, L. B. Smith 14717 ( FLOR) ; Laranjeiras do Sul, 01 May 1957, G. Hatschbach s.n. ( RB 100591 ) ; Ponta Grossa, December 1969, P. L. Krieger 8135 ( RB). Rio Grande do Sul: Cruz Alta , 28 April 1988, J. Mattos 31602 ( HAS) ; Espumoso, Depósito , 28°53’05.6”S, 52°48’03.1”W, 07 February 2019, A. L. Christ 556 ( ICN) ; Passo Fundo , April 2009, M. Savaris 69 ( ICN) ; Pinheiro Machado , 28°16’47”S, 53°02’32”W, s.d., D. F. Silva ( ICN 197154 ) ; Porto Alegre, Morro São Pedro , 17 March 2017, A. L. Christ 362 ( ICN) ; Santa Maria, Distrito de Santo Antão , 04 March 2015, J. Schaefer 418 ( SMDB) ; Viamão, 12 March 2011, S. Bordignon s.n. ( ICN 167287 ). São Paulo: Botucatu , 27 February 1975, I. Gottsberger 33-27275 ( R) ; Itapetininga , 13 April 1947, J. I. de Lima s.n. ( RB 60654 ) . PARAGUAY. Alto Paraná: Ñacunday, s.d., J. E. Montes 11001 ( LP). Amambay: Pedro Juan Caballero , March 1934, T. Rojas 6709 ( LP). Caazapá: Santa Ursula, s.d., A. Schinini 27845 ( SI). Cordillera: Eusebio Ayala, s.d., E. Zardini 47691 ( SI). San Pedro: Primavera, s.d., A. Woolston 1232 ( SI) .

Figures

FIGURE 5.A–F. Chromolaena nervosa.A.Specimen growingin itsnaturalhabitat.B.Leaf size variation.C. Branches andcapitulescences. D. Capitula. E. Details of indument of the adaxial surface of the leaves. F. Details of indument and venation of the abaxial surface of the leaves. Image credits: Martin Grings (A–C, E–F) and Anderson Christ (D).