A new synonym of Rhododendron subgenus Hymenanthes (Ericaceae)

Morphological comparison indicate s that Rhododendron oligocarpum is conspecific with R. leishanicum. Therefore, we reduced R. oligocarpum to a synonym of R. leishanicum.

Rhododendron, Rhododendron leishanicum, morphology, new synonym Rhododendron L. is the largest genus of Ericaceae, which c ontains ca. 1200 species (Chamberlain et al. 1996; MacKay and Gardiner 2017). This genus is widely distributed the Asia, Europe and North America, of which the great majority occurs in China and the Malaysian archipelago, the centers of diversity are in the Himalayas and South East Asia (Fang et al . 2005; Gibbs et al . 2011). When we revised the type specimens of Rhododendron from Guizhou Province, China, R. leishanicum Fang et S. S. Chang ex Chamb. and R. oligocarpum Fang et X. S. Zhang were found to be morphologically very similar and identified very confusing. Rhododendron leishanicum was originally described by Chamberlain (1982) based on a single collection, Austro-Guizhou Exped 909 , from Leigong mountain in Lei Shan Xian, Guizhou Province, China (Fig. 1A). In the protologue, Chamberlain placed R. leishanicum in the Subsection Williamsiana. The next year, R. oligocarpum was described by Fang (1983) based on six collections (including Z. S. Zhang et al 401557 (Typs), Z. S. Zhang 58, T. H. Tu 31739, from Fanjing Mountain ; Austro- Guizhou Exped 1411, from Leigong Mountain ; G. Z. Li 6211 & 11277, from Maoer Mountain) from three different origins in China (Fig. 1B-D). According to the protologue, Fang placed R. oligocarpum in the Subsection Maculifera. Meanwhile, R. leishanicum was again described as a new species by Fang in the same protologue. It is worth noting that a paratype of R. oligocarpum , Austro -Guizhou Exped 1141, was collected from Leigong Mountain (Fig. 1C) , but the relationship between R. oligocarpum and R. leishanicum were not mentioned in the protologue. According to critical examination of the type specimens and original descriptions of R. leishanicum and R. oligocarpum , we found that both species have tomentose young branches and petioles, with small apiculate leathery leaves, racemose-umbellate inflorescences, campanulate corolla, filaments pubescent at base, ovoid ovaries (Table 1). Therefore, we place R. oligocarpum in synonymy with R. leishanicum according to ICN rules (Turland et al. 2018). Taxonomy treatment Author-formatted, not peer-reviewed document posted on 08/03/2024. DOI:  https://doi.org/10.3897/arphapreprints.e122409 Rhododendron leishanicum Fang et S. S. Chang ex Chamb. (1982: 261). Type:—CHINA. Guizhou province: Leishan Xian, L eishan, 1850 m, 29 april 1959, Austro-Guizhou Exped 909 (holotype: SZ; isotype: HGAS007912!; KUN0540381!). Rhododendron oligocarpum Fang et X. S. Zhang (1983: 466). syn. nov. Type: —CHINA. Guizhou province: Yinjiang county, Sanduodian, 2070 m, 14 april 1964, Z. S. Zhang et al 401557 (holotype: HGAS0088928!; isotypes: IBSC0481928!; PE01297915!, PE01297916! ; paratype: HGAS007915!; IBK00187538!; IBK00187539!; IBK00187541!; IBK00187559!; PE00312607!; PE00313389!; KUN540382!; SZ0036179!). Description. Shrubs or small trees, 3 -6 m tall; bark gray, dehiscent on drying; branchlets terete, 3 -4 mm in diam., setose when young, grad -ually glabrescent; bud scales membranous, long-ovate, 1-1.5 × 0.5-0.7 cm, apex rounded or with short cusp, with yellowish hairs on outer surface, inner surface glabrous. Petiole rounded abaxially, furrowed adaxially, 5-15 mm, densely setose; leaf blade leathery, elliptic or obovate, 4- 6 × 2-3 cm; base rounded or subcordate; margin revolute, apex rounded, with small apiculate; abaxial surface pale green, glabrous or sometimes sparsely hairy on midrib; adaxial surface green, sparsely glandular; midrib impressed abaxially, grooved adaxially; lateral veins 11 -15-paired, inconspicuous on both surfaces. Inflorescence racemose-umbellate, 3-5-flowered; rachis 5-7 mm, tomentose. Pedicel 1-2 cm, densely setose-tomentose; calyx teeth 5, 1 -2 mm; corolla campanulate, purple -red, with deep purple basal spots, 3 -3.5 cm, lobes 5, sub -orbicular, ca. 1.5 × 2 cm; apex emarginate; stamens 10, unequal, 1–2 cm, filaments pubescent at base, ovary cone-shaped, 4-5 mm, densely setulose -tomentose; style 2.5 -3 cm, glabrous, stigma slightly expanded. Capsule cylindric, 20-25 × ca. 7 mm, rough. Flowering from April to May and fruiting from September to October. Distribution and habitat. Rhododendron leishanicum is distributed in Eastern Guizhou and Northeastern Guangxi. It grows in Thickets at 1800-2500 m a.s.l. Specimens examined. China. Guizhou: Qiandongnan Prefecture, Leigong Mountain, P . L. Song 1016 (GYBG barcode 0002282, 0002283), 4407 (CCNU barcode 9018123), 4717 (CCNU barcode 9018122); Tongren City, Fanjing Mountain, Z. S. Zhang et al 401673 (IBSC barcode 0481934), 401317 (HGAS barcode 0088940, IBSC barcode 0481929), 400681 (HGAS barcode 0088933), 400610 (HGAS barcode 0088939), Z. P . Jian 32039 (HGAS barcode 0088938), Wuling Mountain Expedition 731 (GFS barcode 0007355, KUN barcode 0339467, 0339468, PE barcode 00258535), 1348 (GFS barcode 0007356, KUN barcode 0339469). Guangxi: Guilin City, Maoer Mountain, G. Z. Li 11272 (IBK barcode 00187540), 12378 (IBK barcode 00187542), 12084 (IBK barcode 00187561), F . X. Jin 1066 (HTC barcode 0010523, 0010524, 0010525), J. X. Zhong 83311 (IBK barcode 00187551, 00187552, IBSC barcode 0481913), 83523 (IBK barcode 00187560), 81647 (IBK barcode 00187566, 00187567), L. M. Gao 20077 (KUN barcode 0767388, 0767389). Author-formatted, not peer-reviewed document posted on 08/03/2024. DOI:  https://doi.org/10.3897/arphapreprints.e122409

We thank the curators of PE, IBSC, KUN, IBK, SZ and HGAS for allowing us to examine specimens or use images of specimens and the National Specimen Information Infrastructure (NSII , https://www. nsii.org.cn/2017/) for availability of digitized specimens. Additional information Conflict of interest The authors have declared that no competing interests exist. Ethical statement No ethical statement was reported. Funding This study was supported by Young Scientists Fund of Guizhou Academy of Sciences (Qiankeyuan Key -J [2024] 15) and National Natural Science Foundation of China (31160037) and Guizhou Provincial Basic Research Program (Natural Science)-Study on the Type Specimens of Vascular Plants in Guizhou Based on DELTA System (Qiankehe Fundamentals-ZK [2023] General 234). Author contributions Conceptualization: XC, LH, SC. Data curation: JMY, JXL, YSH . Writing – original draft: SC, LH, XC. Writing - review and editing: SC, XC. Author ORCIDs Sheng Chen https://orcid.org/0000-0002-2727-6504 Lei Hao https://orcid.org/0009-0001-0276-6523 Jun-Mei Yuan https://orcid.org/0009-0007-1861-5790 Jia-Xin Lou https://orcid.org/0009-0005-9845-1655 Yun-Song He https://orcid.org/0009-0002-8791-558X Xiang Chen https://orcid.org/0009-0008-0773-4978 Data availability All of the data that support the findings of this study are available in the main text.

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