Molecular and morphological analyses clarify species delimitation in section Costatae and reveal Betula buggsii sp. nov. (sect. Costatae, Betulaceae) in China

Abstract

Background and Aims Delineating closely related and morphologically similar species is difficult. Here, we integrate morphology, genetics, ploidy and geography to resolve species and subspecies boundaries in four trees of section Costatae (genus Betula): Betula ashburneri, B. costata, B. ermanii and B. utilis as well as multiple subspecies and polyploid races. Methods We genotyped 371 individuals (20-133 per species) from 51 populations at 15 microsatellite markers, as well as a subset of individuals using restriction-site associated DNA sequencing and nuclear internal transcribed spacers. We determined the ploidy level of eight individuals using flow cytometry and characterized leaf variation for a subset of 89 individuals by morphometric analysis. Key Results Integration of multiple lines of evidence suggested a series of revisions to section Costatae taxonomy. Betula costata and B. ermanii were found to be valid. Molecular and leaf morphology analyses revealed little differentiation between diploid B. albosinensis and some samples of B. utilis ssp. utilis. Whereas other B. utilis ssp. utilis samples and ssp. albosinensis formed a morphological continuum but differed based on genetics. Specifically, B. utilis ssp. albosinensis was divided into two groups with group I genetically similar to B. utilis ssp. utilis and group II, a distinct cluster, proposed as the new diploid species Betula buggsii. Phylogenomic analysis based on 2,285,620 SNPs identified a well-supported monophyletic clade of B. buggsii. Morphologically, B. buggsii is characterized by elongated lenticels and a distinct pattern of bark peeling and may be geographically restricted to the Qinling-Daba Mountains. Conclusions Our integrated approach identifies six taxa within section Costatae: B. ashburneri, B. buggsii, B. costata, B. utilis ssp. utilis, B. utilis ssp. albosinensis and B. ermanii. Our research demonstrates the value of an integrative approach using morphological, geographic, genetic and ploidy level data for species delineation.

A nearly 30-years living collection from the Royal Botanic Garden Edinburgh is a new species: a case study ofBetula mcallisteriisp. nov. (sect.Acuminatae, Betulaceae) and its little hybridization withBetula luminifera

“…Seventy additional ITS sequences from Betulaceae (Wang et al, 2022; Wang et al, 2016) were included to infer the phylogenetic position of the “unidentified sample”. A total of 95 sequences were aligned using BioEdit v.7.0.9.0 (Hall, 1999) with default parameters.…”

“…We performed flow cytometry following Wang et al (2022) for three accessions of the "unidentified sample" collected from populations NSX and XYB. We also inferred the ploidy of the 86 samples sequenced in this study using the method described in Zohren et al (2016).…”

“…To delineate species more reliably, an integrated approach has been increasingly adopted, combining morphological, molecular and (-or) cytogenetic data (Alors et al, 2016; Fujita et al, 2012; Newton et al, 2020; Wang et al, 2022). The advantage to use an integrated approach for species delimitation is to overcome the subjective species concepts (Carstens et al, 2013; Hausdorf, 2011; Hey, 2006).…”

“…In plants, diploid and tetraploid close relatives usually have a strong reproductive isolation as triploids are mostly sterile, impeding interspecific gene flow (Fowler & Levin, 1984; Husband & Sabara, 2004; Levin, 1975; Roccaforte et al, 2015). Nowadays, an increasing number of studies use an integrated approach to delimitate taxa and describe new species (Barrett & Freudenstein, 2011; Wang et al, 2022). The rapid development of next-generation genotyping allows for characterizing new species confidently as using hundreds and thousands of single nucleotide polymorphisms (SNPs) not only allows for robustly inferring the phylogenetic position but also for confidently estimating population genetic structure and inferring ploidy level indirectly (Cariou et al, 2013; Grewe et al, 2017; Zohren et al, 2016).…”

Betula mcallisteri sp. nov. (sect. Acuminatae, Betulaceae), a new diploid species overlooked in the wild and in cultivation, and its relation to the widespread B. luminifera

“…To delineate species more reliably, an integrated approach has been increasingly adopted, combining morphological, molecular, and (or) cytogenetic data ( Fujita et al., 2012 ; Alors et al., 2016 ; Newton et al., 2020 ; Giacò et al., 2022 ; Wang et al., 2022 ). The advantage of using an integrated approach for species delimitation is that it overcomes the subjective species concepts ( Hey, 2006 ; Hausdorf, 2011 ; Carstens et al., 2013 ) .…”