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

Abstract

The Gnaphalieae (Asteraceae) are a cosmopolitan tribe with around 185 genera and 2000 species. The New World is one of the centers of diversity of the tribe with 24 genera and over 100 species, most of which form a clade called the Lucilia-group with 21 genera. However, the generic classification of the Lucilia-group has been controversial with no agreement on delimitation or circumscription of genera. Especially controversial has been the taxonomic value of achenial trichomes and molecular studies have shown equivocal results so far. The major aims of this paper are to provide a nearly complete phylogeny of the Lucilia-group at generic level and to discuss the evolutionary trends and taxonomic significance of achenial trichome morphology. We conducted a phylogenetic analysis of the New World Gnaphalieae with nrDNA (ETS, ITS) sequence data from a sampling of 18 genera of the Lucilia-group and utilized these results to examine morphological evolution of achenial trichome types and presence of apical myxogenic cells. Seven well-supported subclades can be recognized within the Lucilia-group (L1-L7). These results support Brazilian and Andean Berroa, Facelis, Lucilia, and Micropsis forming a clade (L1), the inclusion of Chilean Lucilia under Belloa (L2), the monophyly of Stuckertiella + Gamochaeta + Gamochaetopsis (L3), Chevreulia + Cuatrecasasiella (L4) and Antennaria (L5) excluding Antennaria linearifolia, which is resolved in a monophyletic group together with Jalcophila, Loricaria and Mniodes (L6), and the recognition of Gnaphaliothamnus (L7) removed from Brazilian taxa of Chionolaena (L2). Ancestral character state reconstruction of achenial trichome morphology suggests that clades are homogeneous in terms of trichome type, but with exceptions that make it highly homoplastic. Conversely, our results suggest that the presence of myxogenic apical cells is less homoplastic and that closely related species tend to resemble each other more than expected under random variation.