Taxonomy of dark- and white-barked birches related to Betula pendula and B. pubescens (Betulaceae) in Ukraine based on both morphological traits and DNA markers

Abstract

Distribution, taxonomy, nomenclature and molecular genetic data are presented for two closely related pairs of birch taxa: (1) dark-barked Betula pubescens var. sibakademica (Baran.) Kuzeneva (basionym B. sibakademica Baranov) and white-barked B. pubescens var. pubescens, and (2) dark-barked B. kotulae Zaverucha = B. pendula var. obscura (Kotula ex Fiek) Olšavská (basionym B. obscura Kotula ex Fiek, heterotypic synonym B. kotulae) and white-barked B. pendula, respectively. Using published data and sequences obtained in this study, it was found that, although these pairs can be distinguished not only by morphological characters but also by two diagnostic single nucleotide polymorphisms (SNPs) in the internal transcribed spacers ITS1 and ITS2, no sequence differences within each pair were detected. These results suggest that the colour of the bark cannot be used as a taxonomic trait at the species level, and the dark-barked birches within each pair should not be treated as separate species or varieties, but as forms, respectively. Therefore, we reassessed the taxonomic status of B. sibakademica and B. kotulae using morphological traits and molecular genetic markers and suggest that B. pubescens f. sibakademica (Baranov) Tarieiev comb. nov. and B. pendula f. obscura (Kotula ex Fiek) Tarieiev comb. nov. should be used for them, respectively. Betula pubescens f. sibakademica was described in Ukraine for the first time.

ITS secondary structure reconstruction to resolve taxonomy and phylogeny of the Betula L. genus

“…To analyse the impact of rRNA secondary structure on the topology of the phylogenetic tree and support of the clades the following four methods of phylogenetic analysis were performed: (1) Bayesian analysis using an identical number of iterations and 4 by 4 GTR+I+G model suggested by the ModelTest in PAUP v.4.0a (http://paup.phylosolutions. com; Swofford, 2003) for all the regions, (2) neighbor-joining (NJ) clustering in ProfDist (Friedrich et al, 2005;Wolf et al, 2008) using GTR model, 1000 bootstrapping iterations and rate matrix Q for ITS2 in case of considering secondary structure or rate matrix Q for Chlorophyta in case of not considering secondary structure, (3) maximum parsimony (MP) analysis using PAUP v.4.0a with GTR+I+G model, 1000 bootstrap iterations, and 12-letter coding of secondary structure performed using 4SALE, 4) maximum likelihood (ML) analysis using MEGA X without considering secondary structure and R script provided with 4SALE package (http://4sale.bioapps.biozentrum.uni-wuerzburg.de/mlseqstr.html) together with 12-letter coding to consider the structure. It should be noted that 12-letter coding does not include IUPAC codes for ambiguous nucleotides, and, therefore, some information is lost, especially in case of considering hCBCs.…”

“…In addition, there was a recent study of the genetic structure and hybridization of some birch species across Eurasia that provided new data regarding the hybridization patterns and the origin of B. pubescens ( Tsuda et al, 2017 ). Some birch taxa were recently reassessed with propositions to lower taxonomic ranks using also internal transcribed spacers (ITS) as molecular genetic markers (e.g., Kuneš et al, 2019 ; Tarieiev et al, 2019 ; Jadwiszczak et al, 2020 ; Linda et al, 2020 ).…”

“…ITS are among the most common phylogenetic markers in plants including also several studies on birch genus ( Chen, Manchester & Sun, 1999 ; Li, Shoupa & Chen, 2005 ; Wang et al, 2016 ; Kuneš et al., 2019 ; Tarieiev et al, 2019 ). There is a large number of ITS sequences deposited and freely available in the NCBI GenBank, ITS2, and EMBL databases.…”

Short notice concerning the current conservation status of dark-barked birch taxa and the proposed changes to the next edition of the Red Book of Ukraine

“…The research included a corresponding type specimen of B. kotulae (KW 006426; for the whole list of birch types kept in KW see Olshanskyi et al, 2016) and authentic material of B. sibakademica (LE 01041129 and LE 01041130). For more detailed information on these samples, see Tarieiev et al (2019). As a result of the study, we identified the occurrence of two dark-barked birch taxa in Ukraine and proposed to treat them as forms B. pendula f. obscura (Kotula ex Fiek) Tarieiev and B. pubescens f. sibakademica (Baranov) Tarieiev in accordance with the current definitions of infraspecific taxa (Christensen, 1987;Cronquist, 1988;Hamilton & Reichard, 1992).…”

“…To resolve this controversy briefly mentioned above, we have done our own investigation based on herbarium material and data morphology, distribution, occurrence, and sequences of both internal transcribed spacers ITS1 and ITS2, which were analyzed in samples collected from the living trees in Ukraine (Tarieiev et al, 2019). ITS1 and ITS2 are molecular-genetic markers commonly used in plant phylogeny (Mai & Coleman, 1997;Coleman, 2000Coleman, , 2003Coleman, , 2007Coleman, , 2009Wolf et al, 2013).…”