STANFORD, ALICE M.* AND CLIFFORD R. PARKS. Division of Science and Mathematics, University of the Virgin Islands, St. Thomas, VI 00802, and CB#3280, Biology, University of North Carolina, Chapel Hill, NC 27599-3280. - Phylogeny of Castanea (Fagaceae) based matK sequence data.
The current range of Castanea Mill., a Tertiary disjunct genus
with about seven species, includes eastern and western Asia, Europe,
and eastern North America. The similarity between the forests of
eastern Asia and eastern North America has been of interest to
botanists since the time of Linnaeus. The disjunct taxa involved are
hypothesized to have undergone restriction of a formerly continuous
range during the Tertiary period, nearly 15 million years ago. At
that time a global cooling and drying trend forced temperate forests
to migrate southward. We sequenced cpDNA region matK and its
surrounding spacers for all seven Castanea species, and the
sequence data were used to construct a phylogenetic hypothesis for the
genus. Percent sequence divergence between species of Castanea
varies from 1.6 to 4.0%. Phylogenies generated by this work indicate
that the previously proposed intrageneric classification systems
within Castanea do not reflect the evolutionary relationships
of the constituent species. Mapping the distribution of these plants
onto the phylogenies generated by this study supports a complicated
biogeographic history for this disjunct genus. The distribution of
these plants has been thought to be the result of a simple range
restriction, but our data support a more complicated history of
repeated migrations, resulting from a combination of geographic and
climatic factors.
Key words: biogeography, Castanea, disjunct, Fagaceae, matK, Tertiary