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

Abstract

Gamochaeta(tribe Gnaphalieae, Asteraceae) iscomposed of ca. 60 species primarily distributed in tropicaland subtropical America. Within the tribe Gnaphalieae, thegenus is characterized by capitula arranged in spikes orhead-like clusters, few hermaphroditic central florets,truncate style branches with apical sweeping trichomes,pappus bristles connate at the base into a ring falling as aunit, and achenes with globose twin trichomes. Previousmolecular phylogenetic studies have suggested the para-phyly of the genus, but have not provided a basis forredefining 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 ana-lyzed from a broad taxon sample representing the full rangeof morphological variation known in the genus. Our resultsaffirm thatGamochaetais paraphyletic as presently cir-cumscribed. Two clades can be recognized: one clade thatincludes the majority of the species currently assigned toGamochaetaand a second clade that includesGamochaetopsis,Stuckertiellaand seven species ofGamochaeta.We present here a new circumscription ofGamochaeta, including two new combinations,Gamo-chaeta alpinaandGamochaeta peregrina,and the resur-rection ofGamochaeta capitata. Our results also showOmalotheca supina,O. norvegicaandO. sylvatica, whichwere placed by some authors inGamochaetaor inGnaphalium, form a monophyletic group distantly relatedto both genera.