Austroeupatorium steviifolium (DC.) Mailhos &Bonif., 2025

Mailhos, Ary, Cosse, Mariana, Pérez, Camilo & Bonifacino, José Mauricio, 2025, Taxonomic revision of Austroeupatorium (Compositae, Eupatorieae) in Uruguay: new records and a new combination, Phytotaxa 683 (2), pp. 119-132 : 127-129

Austroeupatorium steviifolium (DC.) Mailhos &Bonif. , comb. nov. (urn:lsid:ipni.org:names:77343733-1). Eupatorium steviifolium Candolle (1836: 158), as “steviaefolium”. Type:— Brazil. São Paulo, 1833, F. Sellow, Herb. Imp. Bras. 496

(holotype, P [P00742672!]; isotype G-DC [G00494149!]). ( Fig. 3 C, F ; Fig. 5 )

= Eupatorium steviifolium var. angustius Candolle (1836: 158) . Eupatorium tweedieanum var. angustius (DC.) Malme (1931: 31) . Type:— Brazil. Rio Grande do Sul, 1833, F. Sellow d1186, Herb. Imp. Bras. 806 (holotype, P [P02407945!]; isotype G-DC [G00494148!]).

Subshrubs 0.5–1.5(–2) m tall, stems erect, branched from the base, cylindrical, pubescent; young stems also glandular. Leaves mostly opposite, alternate in inflorescences, 32–63 x 5–15 mm, petioles 2–6(–15) mm long, laminas narrowly ovate or elliptic, entire, base attenuate, apex acute, pubescent on the adaxial surface, sometimes very sparsely glandular, densely pubescent and glandular on the abaxial surface, with three prominent veins from or near the base, herbaceous, slightly discolorous, margin subentire or serrate, slightly revolute. Capitula homogamous, numerous, grouped in terminal corymbiform capitulescences, peduncles 1–6.5(–10) mm long, pubescent, with ascending trichomes, bracts 0 to 2 on peduncles, narrowly oblong. Involucres 5–6 x 3.5–5 mm, campanulate, subimbricate, phyllaries in 3 or 4 series; outer phyllaries narrowly oblong or elliptic, base truncate, apex acute, pubescent and glandular, membranaceous, margin undifferentiated, ciliate; inner phyllaries narrowly obovate, base attenuate, apex rounded, pubescent and glandular at the apex, membranous, margin membranous, ciliate. Receptacles epaleate, convex, foveolate. Florets 29 to 39, perfect; corollas tubulose, funnelform, 3.2–4 mm long, white, rarely pinkish, glandular at the base, lobes 5, 0.3–0.5 mm long, broadly ovate, externally glandular; anther collars oblong, anthers 1.2–1.5 mm long, base obtuse, connective appendage ovate, apex rounded; styles 4.6–6.3 mm long, base straight, papillate, style branches 2.3–3.3 mm long, filiform, papillate, stigmatic surfaces 0.8–1.5 mm long, sterile appendage 1.5–2.3 mm long. Cypselae 1.4– 2. 5 mm long, obpyramidal, 5-nerved, surfaces glandular or glabrous, black; carpopodia symmetric-cylindrical, longer than wide, 0.2–0.5 mm long with subquadrate and oblong cells. Pappus 2.4–3.8 mm long, composed of 30 to 42 white, scabrid bristles, arranged in 1 series.

Distribution and habitat: —Southern Brazil and northwestern Uruguay, in Rivera and Tacuarembó departments ( Fig. 3 ). Austroeupatorium steviifolium grows mostly on wet grasslands on slopes and depressions, and is also frequently found on roadside ditches.

While specimens from Argentina were not found in the herbaria examined during this study, a record uploaded to iNaturalist from Corrientes province ( Gomez 2022) suggests that Austroeupatorium steviifolium is also present in that country. Subsequent herbarium revisions may uncover additional specimens of this species, potentially misidentified as other similar-looking species (see discussion below).

Phenology: —Flowering from March to May; fruiting from April to June.

Discussion: — Eupatorium steviifolium exhibits all morphological traits typical of Austroeupatorium : corolla lobes smooth on the inner surface, anther collar cell walls with transverse annular thickenings, slender and puberulous or papillate style bases, a bristly pappus, and glandular cypselae with distinct carpopodia ( King & Robinson 1970, 1987; Table 1). These traits exclude this species from Eupatorium and also from other morphologically similar genera such as Hatschbachiella , and Stomatanthes , which led us to propose the combination Austroeupatorium steviifolium . This was further supported by the phylogenetic analysis ( Fig. 6 ), in which sampled Austroeupatorium species, including A. steviifolium , resolved as monophyletic with high branch support.

Within Austroeupatorium , A. steviifolium belongs to the group of species with elongated, cylindrical or obconical carpopodia (see King & Robinson 1987). Of these, A. steviifolium mostly resembles A. chaparense ( Robinson 1930: 24) King & Robinson (1970: 433) , A. laetevirens and A. paulinum ( Candolle 1836: 158) King & Robinson (1970: 434) due to their ovate to narrowly ovate or elliptical leaves. However, these species differ from A. steviifolium in the following aspects: Austroeupatorium chaparense has glabrous corollas (vs. glandular in A. steviifolium ); A. laetevirens has glabrescent leaves with one single prominent vein (vs. conspicuously pubescent leaves with three prominent veins in A. steviifolium ); A. paulinum has cuneate leaf bases, which abruptly transition into petioles (vs. attenuate leaf bases gradually transitioning into petioles in A. steviifolium ).

Due to their superficial resemblance, Austroeupatorium steviifolium has often been mistaken in herbaria for A. laetevirens (e.g. K000924851, K000924850), with which it is sympatric throughout most of its distribution, as well as Hatschbachiella tweedieana (e.g. HVAT00002757, MBM435287, MVJB 10450, US 01641610). Indeed, previous reports of Eupatorium steviifolium from Uruguay ( Arechavaleta 1906, Herter 1930) have, upon closer scrutiny, been determined to actually refer to H. tweedieana . Aside from differences in the indumentum of cypselae (setulose and glandular in Hatschbachiella , glandular in Austroeupatorium ), the carpopodium in H. tweedieana is short with subquadrate cells (vs. elongated carpopodia with oblong and subquadrate cells), and its leaves are distinctly petiolate, (vs. leaves with laminas gradually transitioning into petioles in A. steviifolium ). Moreover, both species have strikingly different habitat preferences: H. tweedieana grows mostly on dry soils amid rocky outcrops, while A. steviifolium is frequently associated with humid soils on slopes and depressions.

Across its geographic range, Austroeupatorium steviifolium exhibits considerable diversity in the length-to-width ratio of its leaves. This prompted Candolle (1836) to accommodate this variation into two varieties, E. steviifolium var. steviifolium and E. steviifolium var. angustius . Following our analysis of herbarium specimens and field observations we observed significant variation in leaf shape based on factors such as position along the stem, developmental stage of the plant, or growing conditions, leading to a spectrum of leaf shapes. In light of these findings, and considering that the types of Candolle’s varieties fall within this range of variation, we have chosen not to recognize these infraspecific entities.

Specimens examined: — URUGUAY. Rivera: Paso Tranqueras, March 1945, A. Lombardo 4306 (MVJB 10448). Tranqueras, 7 May 1945, D. Legrand 3974 (MVM). Tranqueras, 1945, A. Lombardo 4360 (MVJB 10450). Cerro al norte del Miriñaque, 7 May 1997, I. Grela et al. s.n. (MVFA 26683). Tranqueras, establecimiento Las Tacuaras, 31°09’20.30’’S, 55°44’01.10’’W, 3 March 2009, C. Brussa & F. Muñoz s.n. (MVJB 27547). Cuñapirú, cerro del Medio, 31°35’16.30’’S, 55°37’25.60’’W, 25 March 2022, A. Mailhos et al. 237 (MVFA). Cuñapirú, base del cerro Miriñaque, 31°32’13.40’’S, 55°37’54.00’’W, 30 April 2023, A. Mailhos & J.M. Bonifacino 430 (MVFA). Ruta 27 km 17, cerro chato Dorado, 31°04’02.80’’S, 55°27’41.60’’W, 27 June 2023, A. Mailhos et al. 448 (MVFA). Ruta 27 km 17, cerro chato Dorado, 31°04’02.10’’S, 55°27’40.70’’W, 8 April 2024, A. Mailhos & P. Pañella 776 (MVFA). Tacuarembó: Ruta 5 km 388, 31°39’47.80’’S, 55°54’30.80’’W, 19 April 2017, C. Pérez et al. 275 (MVFA). Cerro Corona, 31°37’25.00’’S, 55°40’09.10’’W, 14 July 2023, A. Mailhos et al. 463 (MVFA).

Additional specimens examined: — BRAZIL. Paraná: Represa Piraquara, 25°30’50.90’’S, 49°01’28.80’’W, 13 April 2024, M. Bonifacino et al. 7554 ( MVFA). Rio Grande do Sul: Uruguaiana, al sur de João Arregui, 17 May 1963, B. Rosengurtt et al. 9442 ( MVFA). Entre Osvaldo Kroeff y Rocinha, 4 March 1965, R. Brescia & E. Marchesi 4211 ( MVFA). Santa Catarina: Al sur de São Bento do Sul, 26°19’12.10’’S, 49°22’52.10’’W, 14 April 2024, M. Bonifacino et al. 7565 ( MVFA). Al sur de Campo Alegre, 26°19’13.20’’S, 49°13’54.60’’W, 15 April 2024, M. Bonifacino et al. 7570 ( MVFA). Al sur de Campo Alegre, 26°16’52.50’’S, 49°13’09.70’’W, 15 April 2024, M. Bonifacino et al. 7573 ( MVFA). São Paulo: Serra da Bocaina, 22°43’45.00’’S, 44°38’15.00’’W, 12 February 2024, V. Valtierra et al. 496 ( MVFA).

Figures

FIGURE 3. Distribution map of Austroeupatorium species in Uruguay.

FIGURE 5. Austroeupatorium steviifolium. A. Habit. B. Capitula, lateral view. C. Leaf, adaxial surface. D. Leaf, abaxial surface. E. Cypsela.A–E from A. Mailhos & J.M. Bonifacino 430 (MVFA). A–B by J.M. Bonifacino, C–D by A. Mailhos.

FIGURE 6. Maximum likelihood phylogeny of Austroeupatorium and related genera constructed using concatenated ITS and ETS sequences. Support values of 95 or more are shown above and below branches, corresponding to Ultrafast Bootstrap and SH-aLRT tests respectively.