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Trees and shrubs belonging to the Betula L. genus seem to represent one of the most confused interspecific relationships, and hybridization is considered to be one of the main factors responsible for the substantial genetic and morphological variation of birches. In the present investigation, the internal transcribed spacer ITS1 and ITS2 regions of nuclear ribosomal DNA, nuclear alcohol dehydrogenase ( ADH ) gene sequences and amplified fragment length polymorphisms (AFLPs) as well as the Atkinson discriminant function (ADF) of leaf morphology were used to verify hypotheses concerning the origin of the dark barked Betula obscura and B. pendula var. carelica with the patterned wood. Both plants were considered by different authors to be distinct species, intraspecific forms of common B. pendula or B. pubescens , or hybrid taxa between B. pendula and B. pubescens . In the phylogenetic trees, the ITS and ADH gene sequences of both B. obscura and B. pendula var. carelica clustered with those of B. pendula , whereas B. pubescens trees were somewhat distinct. In turn, the AFLPs revealed genetic similarity of B. pendula var. carelica to both frequent species, whereas B. obscura was clearly distinct from other birches. Values of the ADF indices of the rare birches were typical for B. pendula . In the light of the results obtained, we imply that B. obscura and B. pendula var. carelica represent an intraspecific variation of B. pendula , they are neither intraspecific taxa of B. pubescens nor hybrid species between the common birches. Different grouping of B. obscura in the AFLPs and DNA sequences analyses is likely a result of an unreliable phylogenetic signal of the former molecular markers.

Analyses of molecular markers and leaf morphology of two rare birches, Betula obscura and B. pendula var. carelica