It has been controversial whether Betula tatewakiana, a dwarf birch distributed in Hokkaido of northern Japan, is an endemic species or a synonym of B. ovalifolia broadly distributed in northeast Asia. The endemic hypothesis is based on the idea that B. tatewakiana is diploid while B. ovalifolia is tetraploid and that they are separated based on the ploidy level; however, no chromosome data have actually been published before. Resolving the taxonomic problem is crucial also in judging the conservation priority of B. tatewakiana in a global perspective. Our chromosome observation revealed that B. tatewakiana is tetraploid as well as B. ovalifolia. We also conducted morphological observations and clarified that B. tatewakiana is morphologically identical to B. ovalifolia in white hairs and dense resinous glands respectively on adaxial and abaxial leaf surfaces, in which they differ from closely related species in the same section Fruticosae. We conclude that the hypothesis that B. tatewakiana is a Hokkaido endemic based on the ploidy level is not supported and that B. tatewakiana should be merged with B. ovalifolia.

中文翻译：

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基于倍性水平，日本北部的桦木（Betulaaceae）与东北亚卵圆芽孢杆菌的合并

分布在日本北部北海道的矮桦桦桦是地方性物种还是广泛分布于东北亚的椭圆形芽孢杆菌的同义词一直存在争议。地方病假说是基于这样的思想：立陶宛芽孢杆菌是二倍体而卵圆芽孢杆菌是四倍体，并且它们是根据倍性水平分开的。但是，以前从未实际发布过染色体数据。从全球的角度来看，解决分类学问题对于判断立陶宛芽孢杆菌的保护优先性也至关重要。我们的染色体观察表明，立陶宛芽孢杆菌和卵圆芽孢杆菌都是四倍体。我们还进行了形态学观察，并阐明了B. tatewakiana在形态上与B.相同。椭圆叶在白色的毛和浓密的树脂腺体分别在叶的正面和背面，在同一剖面上，它们不同于近缘果的近缘种。我们得出的结论是，不支持基于倍性水平的立枯芽孢杆菌是北海道特有种的假说，而立枯芽孢杆菌应与椭圆形芽孢杆菌合并。