New circumscription of the genus Gamochaeta (Asteraceae, Gnaphalieae) inferred from nuclear and plastid DNA sequences

Abstract

Gamochaeta (tribe Gnaphalieae, Asteraceae) is composed of ca. 60 species primarily distributed in tropical and subtropical America. Within the tribe Gnaphalieae, the genus is characterized by capitula arranged in spikes or head-like clusters, few hermaphroditic central florets, truncate style branches with apical sweeping trichomes, pappus bristles connate at the base into a ring falling as a unit, and achenes with globose twin trichomes. Previous molecular phylogenetic studies have suggested the paraphyly of the genus, but have not provided a basis for redefining generic limits due to incomplete taxon sampling. To address this problem, DNA sequences from the plastid (trnL-F) and nuclear (ETS and ITS) genomes were analyzed from a broad taxon sample representing the full range of morphological variation known in the genus. Our results affirm that Gamochaeta is paraphyletic as presently circumscribed. Two clades can be recognized: one clade that includes the majority of the species currently assigned to Gamochaeta and a second clade that includes Gamochaetopsis, Stuckertiella and seven species of Gamochaeta. We present here a new circumscription of Gamochaeta, including two new combinations, Gamochaeta alpina and Gamochaeta peregrina, and the resurrection of Gamochaeta capitata. Our results also show Omalotheca supina, O. norvegica and O. sylvatica, which were placed by some authors in Gamochaeta or in Gnaphalium, form a monophyletic group distantly related to both genera.

Phylogeny and evolution of achenial trichomes in theLucilia‐group (Asteraceae: Gnaphalieae) and their systematic significance

“…(2016). Gamochaetopsis was also resolved as nested in a clade also including Gamochaeta and Stuckertiella, confirm ing the results of Urtubey & al. (2016).…”

“…-Different studies in past years have contributed to clarifying the phylogenetic relationships in the Gnaphalieae, confirming the placement of the Luciliagroup within the FLAGclade (see Introduction). Relationships of the genera within the Luciliagroup have already been evaluated in previous papers (Freire & al., 2015;Nie & al., 2016;Urtubey & al., 2016), but our study adds species of the Luciliagroup not included in earlier studies.…”

“…Achenes were mounted with one drop of Tween 20 and one drop of Hoyer's Solution was added. In order to characterize all species included in the phylogenetic analysis, we complemented the data with information from the literature, especially for the species outside the Lucilia group, or where achenes were not available for study (Cabrera, 1932;Dillon & Sagástegui Alva, 1986, 1991aAnderberg & Freire, 1990;Anderberg, 1991;Freire, 1993Freire, , 1995Ascensão & al., 2001;GalbanyCasals & al., 2004a;Morefield, 2006;Abid & Qaiser, 2008b;Loeuille & al., 2011;AndrésSánchez & al., 2014AndrésSánchez & al., , 2015Urtubey & al., 2016). Appendix 2 contains a list of sources from which information on achenial trichome morphology was obtained.…”

“…(2015), who basically united Luciliocline and Mniodes. Stuckertiella, which shares many morphological characters with Gamochaeta, is nested in the latter genus and has been treated as synonymous by Urtubey & al. (2016).…”

“…(2015) showed that Luciliocline cannot be phylogenetically distinguished from Mniodes and sunk the for mer into the latter. Gamochaeta has almost unanimously been considered to be closely related to Stuckertiella (e.g., Anderberg, 1991;Dillon, 2003), and the latter was sunk into the former by Urtubey & al. (2016), along with Gamochaetopsis.…”