Chloroplast DNA Variation Shed Light on the History of Lime Tree (Tilia cordata s. l.) in the Eastern Part of the Range

The Quaternary history of European nemoral forests in the east of their distribution may differ significantly from the typical dynamics of populations and ranges of most deciduous species in Western and Central Europe, characterized by survival in the Mediterranean refugia in glacial phases and recolonization in the interglacials. This study focuses on the phylogeography of the small-leaved lime Tilia cordata Mill. s. s. (Malvaceae) and related taxa in Eastern Europe, the Urals, Siberia, and the Crimea. The variability of five chloroplast DNA fragments (CDt, HKt, DT, K1K2, and psbJ–petA) was studied in 29 populations using restriction analysis and sequencing. The deep divergence of the six identified haplotypes and poorly supported topology of the phylogenetic tree presumably correspond to the long existence of T. cordata in several areas of the western Palaearctic isolated from each other. The two haplotypes dominate on the Russian Plain, in the Urals, and in Siberia. Their comparison with the data of other authors shows their absence in Western and Central Europe. Several haplotypes found in western Russia, in Belarus, and in Western Ukraine correspond to haplotypes previously identified in Central Europe and the Carpathians. We assume that such a distribution of chloroplast DNA variability is due to the preservation of lime in the refugia in the east of the range during one or several of the last glacial intervals and recolonization in the Late Glacial on the Russian Plain. Comparison of the results of the study of the variability of chloroplast DNA in T. cordata s. l. and the results of the study of nuclear microsatellites suggest that the species that lived in the Urals and the Russian Plain in the Pleistocene is a Siberian lime (T. sibirica), later displaced by the European small-leaved lime and now occurring only in Southern Siberia.