Towards a better understanding of the Chromolaena congesta complex (Asteraceae, Eupatorieae): updated synopsis with taxonomic novelties Author Christ, Anderson Luiz Author Nakajima, Jimi Naoki Author Ritter, Mara Rejane text Phytotaxa 2025 2025-02-24 689 2 163 184 https://doi.org/10.11646/phytotaxa.689.2.1 journal article 10.11646/phytotaxa.689.2.1 1179-3163 16706769 5. Chromolaena elliptica (Hooker & Arnott) King & Robinson (1970: 200) . Eupatorium ellipticum Hooker & Arnott (1836: 240) . Type :— BRAZIL . Rio Grande do Sul , s.d., J . Tweedie s.n. ( lectotype : K000486789 !, designated by Freire & Ariza Espinar (2014: 332) ; isolectotype GH 00007648 !) . ( Fig. 1J–L ) Distribution: — Argentina ( Corrientes and Misiones provinces), Brazil ( Paraná , Rio Grande do Sul , Santa Catarina and São Paulo states), Paraguay (Central, Itapúa and Paraguarí departments) and Uruguay ( Lavalleja and Rivera departments). This species is typical of dry grasslands from the Río de la Plata grasslands and highland grasslands of the Mata Atlântica domain in southern Brazil . Flowering period: —Flowers mostly from February to April. Conservation status: —Endangered (EN), criteria B2ab(iii). Despite what its range of occurrence would suggest, C. elliptica is known from few populations collected in the last decades. Populations of this species normally are composed of few mature individuals and are fragmented throughout the species range. Furthermore, its preferred environments are under extreme pressure from agriculture and silviculture. Still, some populations are known to be protected in conservation units at least in Brazil , such as the Parque Estadual do Tainhas in Rio Grande do Sul state . Comments: — Chromolaena elliptica is characterized mostly by the decumbent habit, elliptic leaves with cuneate bases ( Fig. 1J–K ), antellate secondary capitulescences and presence of glandular hairs in the phyllaries, florets and cypselae. This set of traits differentiates it from C. rhinanthacea , with which it shares some superficial similarities. Other than that, the most similar species to C. elliptica is C. congesta , and many populations with intermediary morphological traits are known across their distributional range. Studies with molecular phylogenetics and population genetics would be invaluable to better understand the relationship between these species and to determine if these intermediary populations could be the results of hybridization. In any case, these species are currently considered distinct entities and can be distinguished principally by the shape of the outer phyllaries, which are usually cuneate in C. elliptica ( Fig. 1L ) and usually apiculate in C. congesta . Other useful traits to differentiate these species are growing habit (decumbent in C. elliptica vs. erect in C. congesta ) and leaf shape (deltate with truncate or rounded bases in C. congesta ). Selected specimens: — ARGENTINA . Corrientes : Santo Tomé , Estancia Garruchos , 17 February 1960 , T . M . Pedersen 6471 ( LP ). Misiones : Santa Ana , 15 March 1986 , J . L . Fontana s.n. ( SI 130682 ) . BRAZIL . Paraná : Jaguariaíva , PR-151, 24°19’57”S , 49°47’26”W , 05 April 2019 , A . L . Christ 676 ( ICN ). Rio Grande do Sul : Arvorezinha , RS-332, 28°48’16.3”S , 52°15’46.7”W , 07 February 2019 , A . L . Christ 548 ( ICN ) ; Guaíba , Fazenda São Maximiano , 06 April 1976 , N . I . Matzenbacher 503 ( ICN ) ; Giruá , Granja Sodal , March 1964 , K . Hagelund 2033 ( ICN ) ; Jaquirana , Parque Estadual do Tainhas , 19 March 2017 , A . L . Christ 386 ( ICN ) ; Passo Fundo , April 2009 , M . Savaris 60 ( ICN ) ; Porto Alegre , Morro São Pedro , 17 March 2017 , A . L . Christ 370 ( ICN ) ; Nonoai , Rio Uruguai , March 1945 , B . Rambo s.n. ( PACA 28300 ) ; Vacaria , 27 February 1946 , B . Rambo s.n. ( PACA 32351 ). Santa Catarina : Cerro Negro , 27°47’04.0”S , 50°52’36.2”W , 07 March 2019 , A . L . Christ 580 ( ICN ) ; Painel , 28°04’45”S , 50°07’29”W , 28 February 2020 , A . L . Christ 701 ( ICN ). São Paulo : Itapetininga , 26 March 1945 , J . I . de Lima s.n. ( RB 55745 ) ; São Paulo , Vila Ema , March 1940 , A . C . Brade 16176 ( RB ) . PARAGUAY . Central : Caballero , 15 November 1964 , J . Correa Gomes Jr. 1545b ( SP ) ; Paraguarí : Carapeguá , s.d. T . Rojas 3305 ( LP ). Itapúa : Colonia General Delgado , s.d., T . M . Pedersen 3272 ( LP ) . URUGUAY . Lavalleja : Estación retamosa, 06 November 1993 , J . Ren s.n. ( MVFA 21973 ). Rivera : Arroyo del Potrero , 24 February 2017 , V . Valtierra 3030 ( MVFA ) .