Phylogenetic relationships of the Australasian shrubby everlastings Ozothamnus and Cassinia (Asteraceae: Asteroideae: Gnaphalieae).

Abstract

The first comprehensive phylogenetic study of the Australasian shrubby everlastings Ozothamnus, Cassinia, and their satellite genera is presented based on the nuclear ribosomal external and internal transcribed spacer and three chloroplast spacer regions (matK-psbA, psbA-trnH, ycf6-pbsM). While the hypothesis of the monophyly of the sequence copies found in Cassinia cannot be rejected, sequences from Ozothamnus are found to be non-monophyletic in three possible taxonomic circumscriptions of that genus. Cassinia, Calomeria, Odixia and Haeckeria are nested in a narrowly circumscribed Ozothamnus. Ozothamnus section Hebelaena, a sub-shrubby group long recognized as potentially misplaced in the genus, is more heterogeneous than expected and is found to be potentially polyphyletic. Perhaps more surprisingly, a group of four species previously considered part of "core" Ozothamnus is found to be more closely related to other genera. It includes the subalpine "cascade everlastings" of south-eastern Australia. Although many characters traditionally used for the delimitation of genera are homoplasious, connivent involucral bracts and presence of paleae are synapomorphies for Cassinia. Except for the robust shrubby habit, no morphological synapomorphy for core Ozothamnus/Cassinia is currently evident. Future studies are needed to test these results with additional data, to identify morphological and anatomical synapomorphies for individual clades and to resolve species-level relationships with more extensive sampling to address the possibilities of incomplete lineage sorting or reticulate evolution.