Early Phylogenetic Divergence of Gynodioecious Species Warrants the Recognition of Subseries in Styrax Series Valvatae

Abstract—

In Styrax (Ericales: Styracaceae), gynodioecy is known or likely in ten species. A previous morphological analysis of the genus placed these species into a single highly derived clade within S. series Valvatae. In contrast, DNA sequence data from the nuclear ribosomal internal transcribed spacer (ITS) region yielded two distinct gynodioecious clades within the series, one (South American species) as sister to the rest of S. series Valvatae, the other (S. obtusifolius only; Cuba) as phylogenetically nested within a clade of otherwise hermaphroditic species. Here we test these contrasting phylogenetic placements with analyses that include the plastid ndhF-rpl32-trnL, trnL-trnF, trnS-trnG, and trnV-ndhC genic regions in addition to ITS. Results strongly corroborate the phylogenetic positions of the two gynodioecious clades based on ITS data alone. Clade-specific ITS-plastid phylogenetic discordance provides evidence for hybridization and suggests a pattern of reticulate evolution among some of the southern Brazilian species of the series. Our results agree with the prior evidence for convergent evolution among the gynodioecious species associated with floral reduction. Based on our results and long-standing precedent, we re-confer formal taxonomic recognition on the South American gynodioecious clade by dividing S. series Valvatae into two new subseries, Styrax subseries Latifoli and Foveolaria .