Phylogeny of Styrax based on morphological characters, with implications for biogeography and infrageneric classification

It has been suggested that the characters on which the current infrageneric classification of the genus Styrax is based are not reliable. However, to date no alternative classification for the genus has been proposed. To address this problem, a phylogenetic analysis of Styrax was conducted using 34 morphological characters. Parsimony analysis suggested that none of the currently recognized subdivisions of Styrax are monophyletic except section Pamphilia. This section has traditionally been considered a distinct genus but the analysis placed it in a highly nested position, consistent with its recent transfer into Styrax. The biogeographical history of Styrax was inferred with Pitch parsimony analysis and dispersal-vicariance analysis. Results suggest that 1) the presence of Styrax in South America is the result of migration from southern North America; 2) back-migration from South America to North America has occurred in both montane and lowland tropical lineages; and 3) a migration from Eurasia to North America has occurred in four lineages. The phylogeny provides evidence for a single origin of morphological gynodioecy within the genus, a floral reduction series among the gynodioecious species, and a host shift by gall-forming aphids (tribe Cerataphidini) that parasitize Styrax. Included is a revised infrageneric classification based on the phylogeny with a key and descriptions, and the establishment of two new combinations (Styrax; series Cyrta and Styrax series Benzoin).