About 120 plant taxa exhibit amphi-Pacific tropical disjunctions, i.e., endemism in both tropical America and tropical east Asia. The number is inexact because many amphi-Pacific disjuncts have distributions that overlap to some extent with north-temperate patterns of disjunction. This overlap and the presence of north-temperate fossils of currently amphi-Pacific tropical groups suggest that amphi-Pacific tropical disjunctions follow a boreotropical historical pattern with subsequent expansion or relictualism in tropical areas, as opposed to a southern route of migration. However, phylogenetic estimates, which would otherwise provide a test of this idea, are lacking for most amphi-Pacific tropical groups. We used phylogenetic data from the Styracaceae to test the idea of a boreotropical link between north-temperate and amphi-Pacific tropical disjunctions. We compared and ultimately combined the data from previous morphological phylogenetic studies with those from three molecular data sets (rbcL and trnL spacer/intron of chloroplast DNA, and the ITS region of nuclear ribosomal DNA) to 1) estimate the phylogeny through total evidence and 2) infer the biogeographic history of the family in the context of the fossil record. Results generally support a boreotropical pattern as the best explanation for the current and fossil distribution of the Styracaceae. The phylogeny supports an eastern Asian origin for the family and the large, monophyletic genus Styrax, with Styrax secondarily derived in South America, likely from southern North American ancestors. The phylogenetic data support a rare and geohistorically problematic [eastern north America + eastern Asia][western North America + western Asia] pattern within the north-temperate section of Styrax. Morphology suggests that the eastern Asian-eastern North American genus Halesia is monophyletic, but ITS and trnL analyses group the Asian species of Halesia with the strictly Asian genus Rehderodendron. Other amphi-Pacific tropical groups now need phylogenetic study to assess the generality of the boreotropical pattern detected in the Styracaceae.

Key words: biogeography, ITS, phylogeny, Styracaceae, Styrax, trnL