Chromolaena hirsuta (Hooker & Arnott) King & Robinson (1970: 201)

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 : 173-175

7. Chromolaena hirsuta (Hooker & Arnott) King & Robinson (1970: 201) . Eupatorium hirsutum Hooker & Arnott (1836: 239) . Type:— BRAZIL OR URUGUAY. s.l., s.d., J. Tweedie s.n. (lectotype: K000486819!, designated by Freire & Ariza Espinar (2014: 332)). ( Fig. 4D–F )

Distribution: — Argentina (Buenos Aires, Chaco, Córdoba, Corrientes, Entre Rios, Formosa, Misiones, Santa Fé provinces), Brazil (Paraná, Rio de Janeiro, Rio Grande do Sul, Santa Catarina and São Paulo states), Paraguay (Alto Paraguay, Amambay, Caaguazú, Concepción, Cordillera, Guairá, Itapúa, Misiones, Ñeembucú, Paraguarí and San Pedro departments) and Uruguay (in all departments except Flores). Chromolaena hirsuta is extremely common in open environments across its range, and does not seem to have environment preferences, being particularly frequent even in anthropized sites such as wastelands and roadsides.

Flowering period: —Flowers mainly from November to April, with flowering peaks in February and March.

Conservation status: —Least Concern (LC). This species is frequent across its distributional range, with extensive populations composed of numerous mature individuals. Despite observed threats for the conservation of grasslands from both the Rio de la Plata region and the Mata Atlântica domain in Brazil (e.g. Külkamp et al. 2018, Yezzi et al. 2021), C. hirsuta seems to be well adapted to different available environments, including anthropized sites, which is why we consider that this species is not under risk of extinction or particularly threatened by habitat loss.

Comments: —Traditionally, Chromolaena hirsuta has been identified based on its alternate leaves at least in the upper half of the stem (e.g. Cabrera et al. 1996, Perez 2019, Christ & Rebouças 2020) ( Fig. 4D ). However, we observed many specimens and populations with opposite leaves until the capitulescence, but still overall very similar to more “typical populations”. Our recent morphological survey with the C. congesta complex ( Christ et al. 2023a) suggests a broader set of traits to circumscribe C. hirsuta while also accommodating populations with opposite leaves: stems and branches mostly hirsute to villose ( Fig. 4D ); leaves lanceolate to deltate, with acute to attenuate apices and truncate (less commonly rounded) bases ( Fig. 4E ); corymbose secondary capitulescences ( Fig. 4F ); peduncles usually longer than 2 mm long.; and cypselae usually glandular and setulliferous (e.g. Fig. 2C ). These traits are also useful to differentiate C. hirsuta from C. congesta , which is a frequent misidentification error committed by some collectors.

Selected specimens: — ARGENTINA. Buenos Aires: General Pueyrredón , 21 December 1924, A. Valentini 601 ( SI) ; Olavarria , 21 April 1947, A. Krapovickas 3423 ( SP) ; Saladillo , 08 March 1994, M. E. Múlgura 1186 ( SI). Chaco: Tobas, Las Garcitas, 17 January 1947, F. Buratovich 859 ( RB). Córdoba: Punilla, Cerro de la Cruz, 27 March 1942, E. G. Nicora s.n. ( SI 18608 ) ; Rio Seco, 15 March 1987, C. C. Xifreda 620 ( MBM). Corrientes: Ituzaingó , 11 February 1969, A. Krapovickas 14868 ( LP) ; Lavalle, Villa Cordoba, 08 March 1995, A. Schinini 29183 ( SPF). Entre Rios: Concepción del Uruguay , March 1945, A. E. Lanfranchi 364 ( SI). Formosa: s.l., April 1918, P. Jörgensen 2758 ( SI). Misiones: Bonpland, 22 March 1910, F. M. Rodriguez 221 ( SI) ; Candelaria , 08 March 1945, J. E. Montes 602 ( SI) ; San Pedro, Caraguatay, 26 April 1949, J. E. Montes 1564 ( SP). Santa Fé: San Javier , 20 April 1963, G. Martínez Achenbach 805 ( SI) . BRAZIL. Paraná: Balsa Nova, São Luiz do Purunã , 25°28’05”S, 49°38’42”W, 02 April 2019, A. L. Christ 632 ( ICN) ; Jaguariaíva , 12 February 1997, O. S. Ribas 1807 ( PEL) ; Piraí do Sul, Joaquim Murtinho , 24°24’00.9”S, 49°52’11.1”W, 15 March 1999, G. Hatschbach 69041 ( HUCS). Rio Grande do Sul: Caxias do Sul, Criúva, 28°58’06.7”S, 50°59’32.3”W, 13 April 2013, J. Gaio 338b ( HUCS) ; Muitos Capões, PCH Lajeado Bonito , 10 February 2012, M. Verdi 6174 ( FURB) ; Santana do Livramento, Cerro Palomas , 30°49’29.8”S, 55°21’00.7”W, 23 November 2018, A. L. Christ 514 ( ICN) ; Torres , 08 May 2017, A. L. Christ 457 ( ICN) ; Uruguaiana, BR-290, 29°59’31”S, 56°31’37”W, 01 December 2020, A. L. Christ 715 ( ICN). Santa Catarina: Campos Novos , 27°32’39’’S, 51°27’25”W, 19 April 2019, J. F. Richit s.n. ( ICN 200511 ) ; Capão Alto , 17 March 2008, M. Verdi 442 ( PEL) ; Florianópolis, estrada para Jurerê , 15 March 1988, M. L. Souza 1005 ( FLOR) ; Lages, rio Pelotinhas , 02 March 2013, E. D. Santos 14 ( FLOR) ; Painel, 27°55’26.1”S, 50°05’57”W, 03 March 2010, E. K. O. Hattori s.n. ( HUFU 64346 ). São Paulo: Águas de Santa Bárbara , Estação Ecológica de Santa Bárbara , 12 January 2014, G. B. Assis 17 ( RB) ; Iperó, Centro Experimental ARAMAR, 22º23’27”S, 47º37’05”W, 22 March 2017, G. Antar 1404 ( SPF) ; Itararé , 24°07’01.6”S, 49°22’05.3”W, 04 April 2019, A. L. Christ 664 ( ICN) ; São Paulo, Campus da USP, 24 March 2000, D. Sasaki 43 ( SPF) . PARAGUAY. Alto Paraguay: Estancia Roma , March 1917, T. Rojas 2948 ( LP). Itapúa: Encarnación, s.d., T. Rojas 10857 ( LP). Misiones: San Fernando, 05 May 1945, T. Rojas 12634 ( SI) ; San Miguel, 26º28’59”S, 57º04’10”W, 30 November 2000, E. Zardini 55303 ( SPF). San Pedro: Lima, Estancia Carumbe , 24 February 1975, T. M. Pedersen 11167 ( MBM) . URUGUAY. Durazno: Rio Yi , 12 March 1928, W. G. F. Herter 83170 ( SI). Paysandú: Queguay, April 1924, F. Felippone 4865 ( SI). Rocha: Rocha, 02 March 2012, M. Dematteis 4240 ( SI). Soriano: Juan Jackson, March 1936, P. Gallinal B-320 ( SP). Tacuarembó: Tacuarembó, 18 February 2010, M. Dematteis 3746 ( SI) .

Figures

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).

FIGURE 4. A–C. Chromolaena gentianoides. A. Leaves. B. Branches and secondary capitulescence. C. Capitulum. D–F. Chromolaena hirsuta. D. Stem and leaves. E. Details of leaves. F. Capitulescence. G–I. Chromolaena latisquamulosa. G. Growing habit. H. Leaves. I. Capitulum. J–L. Chromolaena rhinanthacea. J. Leaves. K. Detail of stem. L. Capitulum. Scale bars of C, I and L = 2 mm; scale bar of K = 5 mm. Image credits:Anderson Christ (A–C, F–L), Rodrigo Dall’Agnol (D) and Sérgio Bordignon (E).