Phylogeny and Biogeography of the Styracaceae

Abstract

The dicotyledonous family Styracaceae is distributed among all the major Tertiary mixed‐mesophytic forest refugia of the Northern Hemisphere. To infer the biogeographical history of the family and its significance for models of Northern Hemisphere historical biogeography, the phylogeny of the Styracaceae was estimated from separate and combined analyses of three DNA sequence data sets (chloroplast trnL intron/trnL‐trnF spacer, chloroplast rbcL gene, ITS region of nuclear ribosomal DNA) and a morphological data set of 47 characters. Up to 15 samples of other families of Ericales sensu the Angiosperm Phylogeny Group were employed as outgroups. The results strongly support the monophyly of the family. Dispersal‐vicariance analysis and Fitch parsimony optimization support a Eurasian origin of the Styracaceae, with subsequent dispersion to the Americas. This scenario is consistent with a hypothesized European origin for the family based on the fossil record. The eastern Asian–eastern North American disjunct genus Halesia is not supported as monophyletic. The sole Asian species of this genus groups with the Asian genus Rehderodendron, whereas the two North American species most often form parts of polytomies with other genera. The generally nested placement of the warm‐temperate deciduous species of Styrax within the amphi‐Pacific tropical evergreen group is consistent with an initial spread of the genus across the North Atlantic land bridge as part of the Eocene boreotropical flora and subsequent intercontinental dispersion of derived warm‐temperate‐adapted elements.