Short Communication |
Corresponding author: Koh Nakamura ( kohnakamur@gmail.com ) Academic editor: Hanno Schaefer
© 2020 Yuki Shiotani, Tomoko Fukuda, Elena A. Marchuk, Ekaterina A. Petrunenko, Pavel V. Krestov, Svetlana N. Bondarchuk, Yoko Nishikawa, Takashi Shimamura, Yoshiyasu Fujimura, Koh Nakamura.
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Citation:
Shiotani Y, Fukuda T, Marchuk EA, Petrunenko EA, Krestov PV, Bondarchuk SN, Nishikawa Y, Shimamura T, Fujimura Y, Nakamura K (2020) Merger of Betula tatewakiana (Betulaceae) from northern Japan with northeast Asian B. ovalifolia based on ploidy level. PhytoKeys 170: 83-91. https://doi.org/10.3897/phytokeys.170.58585
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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.
Betula, chromosome number, conservation, dwarf birch, endangered species, Hokkaido, Japan, polyploidy, Russian Far East, wetland
Betula ovalifolia Rupr. is a dwarf birch found in wetlands (
The taxonomic problem of B. tatewakiana and B. ovalifolia stems from the confusion in their ploidy level.
In this study, to resolve the taxonomic problem of B. tatewakiana, we focused on the confusion about the ploidy level, because this is the cause of the taxonomic controversy. We conducted chromosome observation and determined the ploidy level. We also conducted morphological observations of B. tatewakiana. Regarding B. ovalifolia, there are two closely related species in the same section Fruticosae, i.e., B. humilis Schrank and B. fruticosa Pall. Betula ovalifolia is distinguished from the two species by white hairs on the adaxial leaf surface (vs. glabrous in B. humilis and B. fruticosa) and by densely resinous glands on the abaxial leaf surface (vs. lack of glands in B. humilis) (
We collected seeds of B. tatewakiana from six and five individuals from Sarabetsu and Nishibetsu mires in Hokkaido, Japan; seeds of B. ovalifolia were collected from one individual in Sikhote–Alin Nature Reserve in Primorsky Krai, Russian Far East (Table
Taxon | Sampling site | Chromosome counts | Voucher no. |
---|---|---|---|
B. tatewakiana | 42°37.33'N, 143°15.72'E, alt. 166 m, Sarabetsu mire, Sarabetsu village, Hokkaido, Japan | 56 | HUBG* 14746 A, E, H |
ca. 56 | HUBG 14746 B, D, F | ||
43°23.36'N, 145°03.66'E, alt. 32 m, Nishibetsu mire, Betsukai town, Hokkaido, Japan | 56 | Yuki Shiotani 1, 26, 29, 30 (SAPT) | |
ca. 56 | Yuki Shiotani 27 (SAPT) | ||
B. ovalifolia | 44°57.31'N, 136°33.01'E, alt. 25 m, Sikhote–Alin Nature Reserve, Terney, Primorsky Krai, Russia | 56 | Koh Nakamura 14198 (SAPT) |
To elucidate whether B. tatewakiana is morphologically identical to B. ovalifolia or not, we observed the key traits in the section Fruticosae: white hairs and dense resinous glands respectively on the adaxial and abaxial leaf surfaces. For B. tatewakiana, specimens examined were the holotype of B. tatewakiana (H. Suzuki and M. Ohki, s.n. with handwriting “Type” and collected on 18 August 1958 as cited in the protologue) in the herbarium of Hokkaido University Museum (
Somatic chromosomes at metaphase were approximately 1.0 µm long in both B. tatewakiana (Fig.
Somatic chromosomes at metaphase of B. tatewakiana and B. ovalifolia. Photomicrographs of B. tatewakiana from Sarabetsu mire (A, 2n = 56: HUBG 14746 A) and Nishibetsu mire (C, 2n = 56: Yuki Shiotani 29), and B. ovalifolia from Primorsky Krai (E, 2n = 56: Koh Nakamura 14198) are shown. B, D, F are drawings of A, C, E, respectively. Scale bar: 5 µm.
The holotype of B. tatewakiana has white hairs and dense resinous glands respectively on the adaxial and abaxial leaf surface (Fig.
Leaf traits of B. tatewakiana and B. ovalifolia. White hairs on adaxial leaf surface (A, C, E) and densely resinous glands on abaxial leaf surface (B, D, F) are shown for the holotype of B. tatewakiana (H. Suzuki and M. Ohki, s.n., A, B), B. tatewakiana of our collection (Yuki Shiotani 38, C, D), and B. ovalifolia in Russia (Koh Nakamura 14188, E, F). Scale bar: 1 mm.
In our chromosome observation, the samples of B. tatewakiana from Sarabetsu and Nishibetsu mires had 2n = 56 (seven samples) and ca. 56 (four samples) chromosomes (Table
Betula ovalifolia Rupr., Bull. Cl. Phys.-Math. Acad. Imp. Sci. Saint-Pétersbourg 15: 378 (1857)
≡ B. tatewakiana M.Ohki & S.Watan., J. Jap. Bot. 34: 329 (1959). Type: Japan, Hokkaido, Sarabetsu village: 18 August 1958, H. Suzuki and M. Ohki, s.n. (holotype,
Type. Russia. Khabarovsk region: Mandshuria, 25 July 1855, R. Maack, s.n. (holotype, LE 01016954!)
Betula tatewakiana is recognized as a synonym of B. ovalifolia as discussed above, and thereby it is not a Japanese endemic species. Hereafter, the Hokkaido populations are called B. ovalifolia. Because B. ovalifolia is broadly distributed in northeast Asia, i.e., Russian Far East, northeast China, North Korea, and northern Japan, the conservation priority of the species may not be high in a global perspective. On the other hand, the Hokkaido populations represent the only island populations disjunct from continental populations. The species had likely moved southward during glacial periods and retreated northward in warmer periods, and the Hokkaido populations are considered to be relict populations (
We thank the staff of the Hokkaido prefecture, Betsukai town, and Sarabetsu village for sampling permission. This study was supported in part by Grants-in-Aid for Scientific Research, KAKENHI to K.N. (16K18596, 20K060870003) and a research grant from the Mitsui & Co. Environment Fund to K.N. (R15-0067).
Specimens for morphological observation:
Betula tatewakiana
JAPAN, Hokkaido: Sarabetsu village, 18 August 1958, (H. Suzuki and M. Ohki, s.n., holotype,
B. ovalifolia
RUSSIA, Primorsky Krai: Terney, 44°57.31'N, 136°33.01'E, alt. 25 m, 22 July 2016, Koh Nakamura 14169–14195, 14197, 14198 (29 specimens, SAPT); Terney, 44°56.85'N, 136°33.00'E, alt. 9 m, 23 July 2016, Koh Nakamura 14289–14297 (9 specimens, SAPT)