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

Abstract

Taxa are traditionally identified using morphological proxies for groups of evolutionarily isolated populations. These proxies are common characters deemed by taxonomists as significant. However, there is no general rule on which character or sets of characters are appropriate to circumscribe taxa, leading to discussions and uncertainty. Birch species are notoriously hard to identify due to strong morphological variability and factors such as hybridization and the existence of several ploidy levels. Here, we present evidence for an evolutionarily isolated line of birches from China that are not distinguishable by traditionally assumed taxon recognition proxies, such as fruit or leaf characters. We have discovered that some wild material in China and some cultivated in the Royal Botanic Gardens Edinburgh, formerly recognized as Betula luminifera, differ from other individuals by having a peeling bark and a lack of cambial fragrance. We use restriction site-associated DNA sequencing and flow cytometry to study the evolutionary status of the unidentified Betula samples to assess the extent of hybridization between the unidentified Betula samples and typical B. luminifera in natural populations. Molecular analyses show the unidentified Betula samples as a distinct lineage and reveal very little genetic admixture between the unidentified samples and B. luminifera. This may also be facilitated by the finding that B. luminifera is tetraploid, while the unidentified samples turned out to be diploid. We therefore conclude that the samples represent a yet unrecognized species, which is here described as Betula mcallisteri.

Cryptic diploid lineage of Betula ermanii at its southern boundary populations in Japan

“…ermanii , and a taxonomic revision is deemed necessary. In this context, the diploid lineages of two tetraploid Betula populations have been described as new species [ 17 , 46 ]. However, mixed-ploidy species, taxa containing at least two ploidies and sometimes odd-number ploidy individuals that originate from hybrids [ 47 , 48 ], have been reported in Betula : B .…”

A cryptic syngameon within Betula shrubs revealed: Implications for conservation in changing subarctic environments

“…However, owing to its morphological resemblance to other shrub birch species, as well as the extensive sympatry observed in their natural ranges, we were aware that the taxonomic validation of dwarf birch could pose challenges. Therefore, the primary objective of our study was to identify congeneric shrub birches (other species) among the sampled individuals through a multicriteria approach, based on morphology and molecular data (genetic diversity and ploidy level assessment), to distinguish and delineate species (Bacon et al., 2012 ; Balao et al., 2020 ; Lissambou et al., 2019 ; Newton et al., 2020 ; Su et al., 2015 ; Wang et al., 2022 ; Zhang et al., 2023 ). We then focus on the biogeography of B. glandulosa and describe its genetic structure.…”