Phytotaxa 387 (3): 177–209 https://www.mapress.com/j/pt/ Copyright © 2019 Magnolia Press Article PHYTOTAXA ISSN 1179-3155 (print edition) ISSN 1179-3163 (online edition) Accepted by Alexander Sennikov: 11 Dec. 2018; published: 9 Jan. 2019 https://doi.org/10.11646/phytotaxa.387.3.1 177 Phylogenetic position of Argentinian and Chilean endemic species of Senecio ser. Culcitium (Asteraceae) with an evolutionary analysis of morphological characters LUCIANA SALOMÓN 1,* , SILVANA M. SEDE 1 & SUSANA E. FREIRE 1 1 Instituto de Botánica Darwinion, Casilla de Correo 22, Labardén 200, San Isidro (B1642HYD), Buenos Aires, Argentina * Author for correspondence (lsalomon@darwin.edu.ar) Abstract In its current circumscription, Senecio ser. Culcitium Cabrera, which includes ca. 40 South American species, is character- ized by discoid, sometimes nodding capitula, calycular bracts resembling a multiseriate involucre, and style branches api- cally truncate with a ring of penicillate collecting hairs. The phylogenetic relationships of Senecio ser. Culcitium were exam- ined based on DNA sequences from ITS and trnK regions, focusing on seven endemic species of Argentina and Chile never included in previous works. Likewise, 18 morphological characters were analyzed and mapped on the phylogeny in order to discuss their importance in defining the group. Our results confirm the polyphyly of S. ser. Culcitium as circumscribed by Cabrera because its members appeared in four different clades throughout Senecio. One clade contains the taxonomic type of the series and about a half of the species previously assigned to S. ser. Culcitium. Most of the Argentinean-Chilean endemic species are split into three different clades distantly related to the principal Culcitium clade: 1) Senecio candidans and S. gil- liesii are nested within S. ser. Hualtatini; 2) S. aspleniifolius and S. jarae are nested within S. ser. Repentes; and 3) S. diemii, S. magellanicus, and S. martinensis appear within the informally named ‘diemii group’. The nodding capitulum, which was traditionally used as a diagnostic character for Culcitium, could be used to define morphologically S. ser. Culcitium in its revised circumscription. However, the other two characters traditionally used as diagnostic, i.e. development of calycular bracts and pubescence of style branches, are variable within the series: the calycular bracts range from scarcely to widely developed and the pubescence of the style branches ranges from a few short hairs poorly differentiated into a crown of hairs to numerous long hairs. As a result of the morphological study of the characters and the phylogenetic analysis, we include a key to differentiate S. ser. Culcitium s. str. from the other series and the informal diemii group, in which the Culcitium spe- cies have been redistributed. Introduction The taxonomy and systematics of the cosmopolitan genus Senecio Linnaeus (1753: 866) have proved to be extremely complex, mainly as a consequence of the morphological variability of its species. Senecio comprised approximately 3000 species in its broader circumscription (e.g. Cabrera 1949, 1985; Jeffrey et al. 1977) or, in the strict sense, ca. 1250 species as redefined by Bremer (1994) and Nordenstam (2007), and ca. 1000 species as estimated by Pelser et al. (2007). The infrageneric taxonomy of the genus Senecio, including the subdivision of South American species into sections and series, has been specifically attended by Cabrera (1939, 1949, 1957, 1985) and Cuatrecasas (1950, 1951). However, the arrangement of these groups has changed throughout the years, even according to the same authors. Following Marhold et al. (2013) who suggest treating large genera, like Senecio, in smaller natural portions for a comprehensive study, we focused our efforts on clarifying Senecio ser. Culcitium Cabrera (1985: 112), first in a taxonomical treatment (Salomón et al. 2018) and then, in this paper, in a phylogenetic study of southern-distributed species. Senecio ser. Culcitium was established on the basis of Culcitium Bonpland (1808: 1), and more recently circumscribed by Cabrera et al. (1999) to include S. section Culcitium Cuatrecasas (1950: 50) and some species previously assigned to S. sect. Repentes Cabrera (1939: 69) (i.e. S. aspleniifolius Grisebach (1879: 207) and S. jarae Philippi (1891: 44)) and S. sect. Brachypappus (Schultz Bipontinus) Bentham & Hooker (1873: 449) p.p. (e.g. S. candidans Candolle, S. serratifolius (Meyen & Walpers) Cuatrecasas). Nowadays, it comprises ca. 40 species distributed in South America from Colombia and Venezuela to the south of Argentina and Chile. This group was morphologically