Chloroplast DNA-Based Phylogeography of Tilia americana (Malvaceae)

Abstract

A comprehensive picture of how plant species and communities move and evolve over time will require that a variety of species be studied, including plants with different life histories, rarity, and distributions. Relatively few phylogeographic studies have focused on trees. In the present study, the phylogeographic history of Tilia americana, American basswood, was investigated. Samples were collected from throughout the United States and Mexican ranges of basswood, and a phylogenetic analysis was conducted based on sequence data from two non-coding chloroplast DNA regions. The results showed no evidence for the various hypotheses of multiple basswood species within the U. S. A., but there is evidence for a divergence between a Mexican and U. S. A. clade within basswood. Population genetics and spatial statistical analyses were also performed, and supported the conclusion that the only significant geographic barrier within the North American basswoods is found between U. S. A. and Mexico. An attempt was also made to interpret the anomalous geographic distribution of certain chloroplast haplotypes, raising further questions about past migration routes of North American temperate forest trees.