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

Luwei Wang; Junyi Ding; James S Borrell; Martin Cheek; Hugh A McAllister; Feifei Wang; Lu Liu; Huayu Zhang; Qiufeng Zhang; Yiming Wang; Nian Wang

doi:10.1093/aob/mcac001

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

Ann Bot. 2022 Mar 23;129(4):415-428. doi: 10.1093/aob/mcac001.

Authors

Luwei Wang^{1

2}, Junyi Ding^{1

2}, James S Borrell³, Martin Cheek³, Hugh A McAllister⁴, Feifei Wang^{1

2}, Lu Liu^{1

2}, Huayu Zhang^{1

2}, Qiufeng Zhang^{1

2}, Yiming Wang^{1

2}, Nian Wang^{1

2

5}

Affiliations

¹ State Forestry and Grassland Administration Key Laboratory of Silviculture in Downstream Areas of the Yellow River, College of Forestry, Shandong Agricultural University, Tai'an, China.
² Mountain Tai Forest Ecosystem Research Station of State Forestry and Grassland Administration, College of Forestry, Shandong Agricultural University, Tai'an, China.
³ Royal Botanic Gardens Kew, Richmond, Surrey, UK.
⁴ School of Life Sciences, Biosciences Building, University of Liverpool, Crown Street, Liverpool, UK.
⁵ State Key Laboratory of Crop Biology, Shandong Agricultural University, Tai'an, Shandong Province, 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 109 individuals by morphometric analysis.

Key results: Integration of multiple lines of evidence suggested a series of revisions to the taxonomy of section Costatae. 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. By contrast, 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 sp. nov. Phylogenomic analysis based on 2285 620 single nucleotide polymorphisms 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, geographical, genetic and ploidy-level data for species delineation.

Keywords: Birch; RAD-seq; flow cytometry; microsatellite markers; polyploidy; species delineation.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Betula* / anatomy & histology
Betulaceae*
China
Diploidy
Polyploidy