Eupatorium xylorhizum Baker (1876: 292)

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 : 166

1. Chromolaena ascendens (Baker) King & Robinson (1970: 199) . Eupatorium ascendens Baker (1876: 296) .

Type :— BRAZIL. s.l., s.d., Herb. C. Martius 798 (lectotype: K000486833 !, designated by Freire &Ariza Espinar (2014: 339); isolectotypes: MO 476730 , NY00168997 !) .

= Eupatorium xylorhizum Baker (1876: 292) , syn.nov. Chromolaena xylorhiza (Baker) King & Robinson (1970: 208) .

Type:— BRAZIL. Minas Gerais, Caldas, s.d., A. F. Regnell I. 210 (lectotype: BR0000005317981 !, designated here; isolectotypes: BR0000006317653 !, BR0000005318308 !, BR0000005318636 !, GH00008058 !, P02406544 !, P00742733 !, P02671635 !, R000006165 !, US00145784!) .

( Fig. 1A–C )

Distribution: —This species is restricted to Brazil, occurring in Minas Gerais, Rio de Janeiro and São Paulo states. Chromolaena ascendens is typical of highland grasslands from mountain ranges in the Mata Atlântica domain. Contrary to what was suggested by Christ & Ritter (2020), this species does not occur in the Brazilian states of Paraná and Santa Catarina, and populations previously identified as this species are likely related to C. congesta .

Flowering period: —Flowers mostly from February to May.

Conservation status: —Endangered (EN), criteria B2ab(iii). Chromolaena ascendens has smaller range when compared to most other species of the C. congesta complex and is usually restricted to highland grasslands from a few mountain ranges in southeastern Brazil. Furthermore, some populations are known only from historical records, and recent collections of this species are not frequent. Many populations are currently protected in conservation units (e.g. Parque Nacional da Serra da Bocaina, Parque Nacional da Serra do Cipó, Parque Estadual da Serra do Ouro Branco), but it would be important to study these populations in order to assert the amount of mature individuals and accompany possible population fluctuations in the next decades.

Comments: — Chromolaena ascendens is unique among the taxa of the C. congesta complex in having a geographic distribution centered in Southeastern Brazil. This species also possesses unique morphological traits as reported by Christ et al. (2023a), e.g. tendency of having smaller involucres (usually less than 6 mm long), cypselae (usually less than 2 mm long) and pappus bristles (less than 4 mm long), while also having fewer bristles (less than 30) and more florets per capitulum (most specimens have 17–24). Other distinct attributes of this species are the villose indument of the stems ( Fig. 1A–B ) and abaxial surface of the leaves, which is seldom observed in other specimens of this complex; leaves orbicular to ovate ( Fig. 1B ); and prevalence of sessile capitula ( Fig. 1C ). Contrary to Christ & Rebouças (2020), the inner phyllaries of C. ascendens are always glandular, while the cypselae may vary from glabrous to setulliferous (e.g. Fig. 2A–B ). The identity of this species was difficult to assert for many decades, with many authors regarding it as a synonym of C. squarrulosa (e.g. Cabrera et al. 1996, Freire & Ariza Espinar 2014, Perez 2019) ( Table 1) and most specimens being misidentified as other taxa of the C. congesta complex or as completely unrelated species. Thus, C. ascendens is a prime example of the importance of taxonomic revisions and integration of multiple types of evidence.

Chromolaena xylorhiza is a new a synonym of C. ascendens , which was first suggested by Christ et al. (2023a).As discussed in this paper, there are no morphological discontinuities between these species, and the traits usually applied to differentiate them (capitulum sessile or not, cypselae glabrous or setulliferous) are variable in most populations. Furthermore, the analyzed type specimens are nearly identical, much like the original descriptions of both taxa are extremely similar, and both taxa co-occur in their entire distribution. We decided to adopt the name C. ascendens for this taxon as it is the most usually used by collectors and researchers. We also provide a lectotypification for E. xylorhizum , as indicated above. We located ten possible syntypes with the collection information in accordance with the protologue of E. xylorhizum (Regnell I. 210, collected in Caldas, Minas Gerais state, Brazil) in herbaria BR, GH, P, R and US plus a negative in F of a specimen deposited in B and probably destroyed. Of these, we selected specimen BR 0000005317981 as a lectotype, as it agrees with the morphological description provided by Baker (1876) and closely resembles most specimens analyzed during our herbaria revisions.

Selected specimens: — BRAZIL. Minas Gerais: Baependi ,APA da Serra da Mantiqueira, 22º23’27”S, 47º37’05”W, 23 February 2009, A. Nogueira 146 ( SPF) ; Catas Altas , 27 April 2001, I. S. M. Gajardo s.n. ( UEC 123462 ) ; Nova Lima , 10 April 1945, L. O. Williams 6547 ( SP) ; Ouro Preto, Serra do Capanema , 20°12’35.5”S, 43°34’27.5”W, 28 February 2008, F. F. Carmo 2412 ( BHCB) ; Poços de Caldas, Morro do Ferro , 08 March 1983, H. F. Leitão 2030 ( HUFU) ; Santana do Riacho, Serra do Cipó , 26 March 1991, J. R. Pirani s.n. ( BHCB 83953 ) ; São Roque de Minas, 19 March 1996, R. Romero , 3323 ( HUFU). Rio de Janeiro: s.l., May 1963, A. P. Duarte 7679 ( PEL) ; Itatiaia , March 1937, A. C. Brade 15600 ( RB). São Paulo: Caieiras, 04 May 1945, W. Hoehne s.n. ( RB 343474 ) ; Campos do Jordão , 26 December 1978, W. Emmerich 53 ( R) ; Mogi das Cruzes, 19 April 1889, Schwacke s.n. ( R 48508 ) ; São José do Barreiro , 19 February 2000, L. Freitas 835 ( UEC) ; São Paulo, Vila Ema , March 1940, A. C. Brade 16171 ( RB) .

Figures

FIGURE 1. A–C. Chromolaena ascendens. A. Detail of stem. B. Habit, stem and leaves. C. Primary capitulescence. D–F. Chromolaena caaguazuensis. D. Stem and leaves. E. Detail of adaxial surface of a leaf. F. Capitulum. G–I. Chromolaena congesta. G. Capitulum. H. Growing habit. I. Details of leaves. J–L. Chromolaena elliptica. J. Growing habit. K. Leaves. L. Capitulum. Scale bar of A = 5 mm; scale bars of G and I = 2 mm. Image credits: Anderson Christ (A, G-H, K-L), Cauê Paiva Vidigal Martins (B-C), Camilo Perez (D–F), Claudenice Dalastra (J) and Sérgio Bordignon (I).

FIGURE 2. Representative cypselae of species of the C. congesta complex portraying morphological variation in diagnostic traits. A. glabrous cypsela (i.e. setae completely or nearly completely absent). B. setulliferous cypsela (i.e. setae visibly present on the ribs and/on between them). C. glandular cypsela (i.e. glandular hairs located at the tips of the arrowheads). Scale bars: 2 mm. Further details on the structure of the cypselae of this species complex are described in Queiroz et al. (2025).