Chromolaena gentianoides (Robinson) King & Robinson (1980: 231)

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

6. Chromolaena gentianoides (Robinson) King & Robinson (1980: 231) . Brickellia gentianoides Robinson (1923: 42) .

Type:— BRAZIL. Rio Grande do Sul, 1816–1821, A. Saint-Hilaire 768, Cat. C² 2739 (lectotype: P0070710!, designated by Christ & Ritter (2018: 112)).

( Fig. 4A–C )

Distribution: — Brazil (Paraná, Rio Grande do Sul and Santa Catarina states) and Uruguay (Rivera department). In Southern Brazil, C. gentianoides is typical of highland grasslands of the Mata Atlântica domain.

Flowering period: —Flowers in March.

Conservation status: —Critically Endangered (CR), criteria B2ab(iii)c(iii). Chromolaena gentianoides is considered extremely rare and in great risk of extinction due to the fluctuation of its known populations and number of mature individuals. Despite being collected in at least four different locations in the last decade, recent fieldwork expeditions have observed that populations of C. gentianoides in Brazil actually consisted of single specimens. Continued expeditions have failed to register growth in these populations, and in fact, some of them seem to have disappeared. The only known location where this species is protected by a conservation unit is in Rio Grande do Sul (Parque Estadual do Tainhas), but that population also included a single specimen, which has not been found again since 2018. We consider important to conduct further fieldwork to search for populations of C. gentianoides , as well as to develop further research to aid in its conservation.

Comments: — Chromolaena gentianoides is characterized by glabrous stems, leaves ( Fig. 4A ), branches ( Fig. 4B ) and its very distinguished involucres, with vinaceous, attenuate involucral bracts ( Fig. 4B–C ). This latter set of characters is useful to differentiate it from C. rhinanthacea , with which this species possesses a great resemblance. Perez (2019) first reports the occurrence of glandular hairs in the abaxial surface of C. gentianoides , a character again observed in a single specimen analyzed in Christ et al. (2023a) and previously not reported by Christ & Rebouças (2020). This morphological trait is considered anomalous and extremely rare in C. gentianoides , however.

Selected specimens: — BRAZIL. Paraná: Curitiba , 20 March 2015, J. M. Santos 8837 ( MBM, SP) ; Piraquara, Fazenda Experimental da Escola de Agronomia, 21 March 1973, N. Imaguire 3210 ( MBM). Rio Grande do Sul: Jaquirana , Parque Estadual do Tainhas , 29°05’11.8”S, 50°21’59.1”W, 03 March 2018, A. L. Christ 501 ( ICN). Santa Catarina: Lages, 27°40’45.7”S, 50°20’08.2”W, 08 March 2019, A. L. Christ 582a ( ICN). Painel, 28°04’45”S, 50°07’29”W, 08 March 2013, E. D. Santos 128 ( FLOR) .

Figures

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).