Preliminary screening of chloroplast markers

Markers showing a high level of intraspecific variability are required for phylogeographic analysis. Eleven chloroplast markers and one nuclear marker were identified from the literature and screened for variation among individuals of Tilia americana s.l. (ranging from n = 5 to n = 14) in North America. Supplementary Table 1 lists the locations where T. americana specimens were collected for the screening. Supplementary Table 2 summarizes the screening results, and indicates that chloroplast markers rpL32-trnL and ndhF-rpL32 produced the largest amount of informative variation. These two markers were then sequenced across a much broader sampling of T. americana for the present study