Genetic and morphometric variability between populations of Betula ×oycoviensis from Poland and Czechia: A revised view of the taxonomic treatment of the Ojców birch

Abstract

Birches are generally known for their high genetic and morphological variability, which has resulted in the description of many species. Ojców birch was described in 1809 by Willibald Suibert Joseph Gottlieb Besser in Poland. Since then, several studies assessing its taxonomy were conducted. Today, various authors present Ojców birch at different taxonomic ranks. In Czechia, the Ojców birch is classified a critically endangered taxon and confirmed at one locality consisting of several tens of individuals. However, before a strategy for its conservation can be applied, we consider it necessary to assess the taxonomic position of the endangered Czech population and to evaluate its relationship to the original Polish population. This study aimed to evaluate the morphometric and genetic variability between populations ofB. ×oycoviensisin Poland and the Czechia and their relationship to regional populations ofB.pendula, one of the putative parental species of the Ojców birch. Altogether, 106 individuals were sampled, including the holotype ofB.szaferi, the second putative parental species ofB. ×oycoviensis, received from the herbarium of W. Szafer, which is deposited at the Institute of Botany in Kraków. Morphological analyses identified differences in leaves betweenB. ×oycoviensisandB.pendula. However, no significant differences were found in genome size between selected taxa/working units except forB.pendulasampled in Czechia. The identified difference of the Czech population ofB.pendulais probably caused by population variability. Genetic variability between all the taxa under comparison, regardless of their origin, was also very low; only the benchmark taxa (B.nanaandB.humilis) clearly differed from all samples analyzed. The results indicate minute morphological and negligible genetic variability between the Czech and Polish populations ofB. ×oycoviensis. In light of our results, the classification ofB.×oycoviensis as B.pendulavar.oycoviensisseems more accurate than all hitherto presented alternatives (e.g.B.×oycoviensisas a separate species).