FRITSCH, PETER W.* AND CYNTHIA M. MORTON. Department of Botany, California Academy of Sciences, Golden Gate Park, San Francisco, CA 94118 and Department of Botany and Microbiology, Auburn University, Auburn, AL 36849. - Phylogeny of the Styracaceae based on four data sets: implications for the historical biogeography of the northern hemisphere and amphi-Pacific tropical disjunctions.
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