Chromolaena caaguazuensis (Hieronymus) King & Robinson (1970: 199)

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 : 167

2. Chromolaena caaguazuensis (Hieronymus) King & Robinson (1970: 199) . Eupatorium caaguazuense Hieronymus (1897: 760) .

Type:— PARAGUAY. Caaguazú, 20 March 1876, B. Balansa 951 (lectotype: G00381975 !, designated by Perez (2019: 14); isolectotypes: BAF, BM000096269 !, BM001043665 !, BR0000005267286 !, G00381976 !, LIL, S-R2102 !) .

( Fig. 1D–F )

Distribution: — Argentina (Misiones province), Brazil (Mato Grosso do Sul state), Paraguay (Amambay, Caaguazú, Central, Paraguarí and San Pedro departments) and Uruguay. Cabrera et al. (1996) also includes the Paraguayan departments of Concepción, Cordillera and Guairá in the geographical extent of this species. The occurrence of C. caaguazuensis in Uruguay was recently reported by Perez (2019), but all specimens we analyzed from this country were misidentified specimens of C. congesta . However, considering that the distribution model produced for this species ( Christ et al. 2023b) supported its occurrence in Uruguay, we decided to include the distributional information provided by Perez (2019). Nonetheless, further fieldwork should be conducted in Uruguay to confirm the occurrence of C. caaguazuensis in this country.

Flowering period: —Flowers from January to May.

Conservation status: —Data Deficient (DD). The true geographical extent of C. caaguazuensis and its estimated AOO are difficult to assert due to the lack of reliable data on the number of populations and the estimates of mature individuals per population. The species is considered rare, as very few recent (i.e. from the last 20 years) collections are known. This is probably a result of most populations being restricted to Paraguay, where herbaria revisions and fieldwork expeditions could not be conducted. Further research on extant populations of C. caaguazuensis is needed before more assertive inquiries on its conservation status can be made.

Comments: — Chromolaena caaguazuensis is recognized mostly by its pendant ( Fig. 1D ), cordate leaves ( Fig. 1E ) and constant number of 4–5 florets in all capitula of the capitulescence (capitulum seen in Fig. 1F ). Superficially, this species is close to C. congesta , and misidentifications between them are extremely common. Despite their similarities, we found that C. caaguazuensis and C. congesta do not co-occur in their geographical range, and that their distributions are limited by different climatic preferences ( Christ et al. 2023b), thus supporting their treatment as separate taxa. Further studies should still be conducted with these species to better understand their relationship and differentiation.

Selected specimens: — ARGENTINA. Misiones: Candelaria , 19 February 1951, J. E. Montes 12341 ( LP) ; Santa Ana , 06 February 1930, F. M. Rodriguez 56 ( LP) ; San Ignacio , 19 March 1986, J. L. Fontana 138-40 ( SI) ; Posadas , s.d., E. L. Ekman 1140 ( LP). BRAZIL. Mato Grosso do Sul: Amambaí, 1979, W. G. Garcia s.n. ( UEC 31440 ) ; Bela Vista, 11 March 2003, G. Hatschbach 74576 ( MBM). PARAGUAY: Amambay: Pedro Juan Caballero , March 1934, T. Rojas 6699 ( LP) ; Zanja Pytá , 09 February 1964, J. C. Gomes Jr. 1503 ( MBM). Caaguazú: Arroyo Guaranunga, 12 January 1991, E. M. Zardini 25965 ( US). Central: Ypacaray, 1913, E. Hassler 12540 ( US). Paraguarí: Carapeguá, s.d., T. Rojas 3355 ( SI). San Pedro: Lima, Estancia Carumbe, 24 February 1975, T. M. Pedersen 11168 ( MBM) .

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).