Generic concepts and species diversity within the Gynoxyoid clade (Senecioneae, Compositae)

Abstract

The Gynoxyoid clade of the Senecioneae (Asteraceae) until now included the five genera Aequatorium, Gynoxys, Nordenstamia, Paracalia and Paragynoxys as diagnosed using selected morphological characters. In their pre-phylogenetic circumscription, the genera Aequatorium and Paragynoxys were considered to inhabit the northern Andes in contrast to Nordenstamia and Paracalia that occur in the central Andes. The most species-rich genus, Gynoxys, was believed to be distributed throughout the Andes. We use a recently established plastid phylogenomic framework that rendered Gynoxys paraphyletic to further evaluate the delimitation of genera in the Gynoxyoid clade. We examine the morphological variation of all members of the Gynoxyoid to identify characters potentially informative at genus level. This results in a matrix of eleven, mostly multistate characters, including those originally used to diagnose these genera. The ancestral character state inference displays a high level of homoplasy, but nevertheless supports the recognition of four genera. Aequatorium is characterised by white radiate capitula. Paracalia and Paragynoxys share white flowers and floral characteristics, such as flower opening and length of disc flowers lobes, as plesiomorphic states, but differ in habit (scandent shrubs vs. trees). Paracalia also retained white flowers, but its two species are characterised by the absence of outer phyllaries. The genera Gynoxys and Nordenstamia comprise species with yellow capitula which appear to be a derived feature in the Gynoxyoids. The genus Nordenstamia, with eight species, is synonymised under Gynoxys since molecular evidence shows its species nested within various parts of the Gynoxys subclade and the morphological variation of Nordenstamia falls well within that of Gynoxys. With the goal to assign all species to four genera (Aequatorium, Gynoxys, Paracalia and Paragynoxys), we assess the states for the eleven characters for all members of the Gynoxyoids and generate new ETS and ITS sequences for 171 specimens belonging to 49 species to further support their generic placement. We provide a taxonomic treatment for the four genera recognised here including amended diagnoses and morphological descriptions. Furthermore, a species-level taxonomic backbone is elaborated for all genera using electronic tools that list 158 currently accepted names and synonyms (209 names in total) with the respective protologue and type information, as well as notes on the current understanding of species limits. Eleven names are newly synonymised, two are lectotypified and eight are newly transferred to other genera.