Cells, Genes & Molecules Taxonomy & Evolution

Species delimitation and a new Betula species in section Costatae

Botanists have developed an integrated approach to identify differences between closely related species.
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Identifying the difference between closely related species can be difficult, particularly when the species themselves have a lot of variation within them. Luwei Wang and colleagues have integrated 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.

A map showing sites of the plants sampled in northeast China.
The distribution of samples used in the study. Source Wang et al. 2022.

The team genotyped 371 individuals 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. They determined the ploidy level of eight individuals using flow cytometry and characterized leaf variation for a subset of 109 individuals by morphometric analysis.

The authors show that species delimitation no longer requires a single criterion. Instead, they use multiple lines of evidence to understand relationships between species. Wang and colleagues write: “Our integrative analyses using different types of molecular markers together with spatial and morphological metadata identified six differentiated clusters, representing six taxa within section Costatae. We argue that with this approach, these six taxa may represent less biased species units. In addition, we identify a new species, B. buggsii, which is morphologically and genetically distinct and monophyletic based on phylogenomic analysis. We suggest that broader application of integrative approaches may have significant advantages in both taxonomy and conservation.”

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Wang, L., Ding, J., Borrell, J.S., Cheek, M., McAllister, H.A., Wang, F., Liu, L., Zhang, H., Zhang, Q., Wang, Y. and Wang, N. (2022) “Molecular and morphological analyses clarify species delimitation in section Costatae and reveal Betula buggsii sp. nov. (sect. Costatae, Betulaceae) in China,” Annals of Botany, https://doi.org/10.1093/aob/mcac001

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