Chromolaena squarrulosa (Hooker & Arnott) King & Robinson (1970: 206)

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 : 178-181

11. Chromolaena squarrulosa (Hooker & Arnott) King & Robinson (1970: 206) . Eupatorium squarrulosum Hooker & Arnott (1836: 239) .

TYPE:— BRAZIL. Rio Grande do Sul, s.d., J. Tweedie s.n. (lectotype: E 00385505!, designated by Freire & Ariza Espinar (2014: 339)).

( Fig. 6A–F )

Distribution: — Argentina (Buenos Aires, Corrientes, Entre Rios, Formosa, Lavalleja, Misiones provinces), Brazil (Rio Grande do Sul and Santa Catarina states), Paraguay (Guairá departments) and Uruguay (Canelones, Cerro Largo, Colonia, Florida, Maldonado, Paysandú, Rio Negro, Rocha, San José, Soriano and Tacuarembó departments). The complete extent of C. squarrulosa in Paraguay is not completely known, but Cabrera et al. (1996) indicates its occurrence also in the Alto Paraná, Amambay, Caaguazú, Canindeyú, Concepción, Cordillera, Misiones, Ñeembucú, Paraguarí and San Pedro departments. Chromolaena squarrulosa is typical of dry grasslands in the Pampa domain in southern Brazil, Uruguay and Argentina, but can also occasionally be found in highland grasslands of the Mata Atlântica domain in southern Brazil.

Flowering period: —Flowers mostly from November to March.

Conservation status: —Least Concern (LC). Chromolaena squarrulosa is recorded in numerous populations across its distributional range, and extreme fluctuations on its AOO, EOO or number of mature individuals per population were not observed. On the other hand, populations are frequently composed of few mature individuals, which are scattered around a larger area, and C. squarrulosa is suffering from habitat loss and fragmentation due to the conversion of natural grasslands into agricultural lots and pasture, mainly in the Pampa domain ( Yezzi et al. 2021). Further habitat fragmentation and loss of populations may eventually lead to a reclassification of this species as Near Threatened, or eventually even in risk of extinction. Still, some populations are known to be under protection in conservation units at least in Brazil (e.g. Parque Estadual do Tainhas) and Argentina (e.g. Parque Nacional El

Comments: —The circumscription of C. squarrulosa has been under debate for several decades ( Table 1), and there are still many questions to be answered before the nature of this species can be completely understood. Many authors have delimited this species in a broad concept, encompassing C. ascendens , C. congesta and C. nervosa , all of them demonstrated to be different species in our studies with integrative taxonomy. However, the morphological limits of this species are still unclear, as there is a noticeable fluctuation in morphological traits and variations across different populations, particularly among populations from highland grasslands in southern Brazil and those of the Pampa domain. Still, our distribution modelling and climate niches analyses ( Christ et al. 2023b) failed to identify different distributional patterns among these populations, and despite their observed morphological discontinuities, our studies have also indicated that morphology alone does not support an interpretation of these populations as separate taxa ( Christ et al. 2023a). Thus, we accept the inclusion of E. ascendens var. parcisetosum Robinson (1923: 9) as a synonym of C. squarrulosa , despite concerns raised on this issue by Christ & Ritter (2019).

Chromolaena squarrulosa can be typically recognized by the squarrose, cinereous outer phyllaries ( Fig. 6A ), which are exclusive to it. However, many populations show variation on this trait ( Fig. 6B–C ), and sometimes a whole set of morphological traits will be necessary to properly identify this species. Other traits useful to its recognition are the sericeous indument of stems and leaves ( Fig. 6D ) (leaves can sometimes be strigose or glabrescent, however ( Fig. 6E )); presence of glandular hairs usually in both surfaces of the leaves; antellate secondary capitulescences ( Fig. 6F ) (sometimes these are absent or corymbose); cuneate outer phyllaries; and cypselae typically eglandular and setulliferous (rarely glabrous or glabrescent) (e.g. Fig 2B ). The occurrence of glandular hairs in the cypselae of C. squarrulosa was reported by Queiroz et al. (2025), but is considered extremely rare, with eglandular cypselae being the most frequent state of character.

Selected specimens: — ARGENTINA. Buenos Aires: Azul, Boca de la Sierra, 37°00’13”S, 59°45’49”W, 17 May 2015, Aballeira 76 ( ICN) ; Tandil, 04 March 1984, J. H. Hunziker 12068 ( SI) ; Tornquist, 02 March 1984, J. H. Hunziker 12038 ( SI). Corrientes: Monte Caseros, 1952, E. G. Nicora s.n. ( SI 132844 ) ; Torrent, s.d. R. A. Spegazzini 403 ( LP). Entre Rios: Colón, 18 January 1976, C. Romanczuk 66 ( SI). Concordia, s.d., A. Burkart 1002 ( SI). Formosa: s.l., October 1919, P. Jörgensen 3352 ( SI). Misiones: Posadas, s.d., E. L. Ekman s.n. ( LP 59737 ) ; San Ignacio, s.d., G. J. Schwarz 5610 ( LP) . BRAZIL. Rio Grande do Sul: Alegrete, Cerro do Tigre , 11 February 1990, D. B. Falkenberg 5191 ( ICN) ; Arroio dos Ratos, Granja Faxinal, 30 November 1977, K. Hagelund 12022 ( ICN) ; Bom Jesus, 08 February 1988, N. Silveira 5230 ( HAS) ; Caçapava do Sul, Pedra do Segredo , 30°32’21.8”S,- 53°33’21.0”W, 21 January 1994, D. B. Falkenberg 6493 ( FLOR) ; Candiota, Mina da CRM , 21 February 2007, R. Wasum 3940 ( HUCS) ; Caxias do Sul, Criúva, 28°52’21.73”S, 51°02’00.08”W, 19 December 2012, J. Gaio 211 ( HUCS) ; Guaíba, Fazenda São Maximiano, 20 January 2009, T. L. S. Alves 30 ( ICN) ; Jaquirana, Parque Estadual do Tainhas , 29°05’13”S, 50°21’56”W, 01 March 2020, A. L. Christ 713 ( ICN) ; Passa Sete, 29°24’18.8”S, 52°52’15.3”W, 09 February 2019, A. L. Christ 562 ( ICN) ; Porto Alegre, Morro da Tapera , 01 April 2021, A. L. Christ 730 ( ICN) ; Quaraí, Cerro do Jarau , 30°11’38”S, 56°29’27”W, 01 December 2016, A. L. Christ 331 ( ICN) ; Rosário do Sul, 30°10’10”S, 55°07’44”W, 29 November 2016, A. L. Christ 321 ( ICN) ; São Francisco de Assis , Gruta São Tomé, 20 April 2008, G. Bruisma 42 ( ICN) ; São Francisco de Paula , Cazuza Ferreira, 11 February 2003, R. Wasum 934 ( HUCS) ; São Pedro do Sul, BR-287, 29°38’42”S, 54°22’57”W, 03 Decmeber 2020, A. L. Christ 723 ( ICN) ; São Vicente do Sul, Cerro do Loreto , 08 February 1990, D. B. Falkenberg 4955 ( FLOR) ; Pelotas, Estação Experimental Florestal do IBOF, 15 January 1981, J. Mattos 22574 ( HAS) ; Unistalda, Serra do Iguariaçá , 23 January 2010 ( SMDB, HUFU) ; Viamão, 30°04’0.25”S, 51°01’22.69”W, 23 October 2008, P. J. S. Filho ( ICN). Santa Catarina: Capão Alto, 28°03’43.1”S, 50°35’16.7”W, 07 March 2019, A. L. Christ 570 ( ICN) ; Lages, SC-114, 27°40’45.7”S, 50°20’08.2”W, 08 March 2019, A. L. Christ 593 ( ICN) ; Painel, 28°04’45”S, 50°07’29”W, 28 February 2020, A. L. Christ 705 ( ICN) . PARAGUAY: Guairá, Yeguanaporá, s.d. J. E. Montes 16570 ( LP) . URUGUAY. Canelones: Tajes, February 1977, E. Marchesi 828 ( MVFA). Cerro Largo: s.l., 31 March 1966, Del Puerto 6177 ( MVFA). Colonia: Los Cerros de San Juan , 20 January 1977, T. M. Pedersen 11581 ( MBM). Florida: Cero Colorado , 17 February 1944, Gallinal PE-5370 ( SP). Maldonado: Sierra de las Animas , 05 April 1968, E. Marchesi 7104 ( MVFA). Paysandú: Orgoroso , 30 December 1997, E. Marchesi s.n. ( MVFA 27387 ). Rivera: Paso Ataques, 31°05’43.6”S, 55°41’23.4”W, 06 January 1998, M. Bonifacino s.n. ( MVFA 27655 ). San José: Ruta 1, 03 January 1969, B. Rosengurt 11077 ( MVFA). Tacuarembó: Arroyo Tres Cruces, 02 February 1962, Del Puerto 1248 ( MVFA) .

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 6. A–F. Chromolaena squarrulosa.A. Typical capitulum. B. Variation of the morphology of the capitulum. C. Corymbose capitulescence and variations of the morphology of the capitula. D. Typical stem and leaves. E. Variation of the morphology of stems and leaves. F. Anthelate capitulescence. Scale bars of A and B = 2 mm. Image credits:Anderson Christ (A–C) and Sérgio Bordignon (D–F).