Based on a critical examination of type specimens, images of living plants, and the literature has shown Rhododendron oligocarpum to be conspecific with R. leishanicum. Although slight variations in corolla colour exist amongst different populations of R. oligocarpum, it does not serve as a key distinguishing trait. Therefore, we reduced R. oligocarpum to a synonym of R. leishanicum, and recommend placing it in Subsection Maculifera.

Morphology, new synonym, Rhododendron, Rhododendron leishanicum

Rhododendron L. which contains ca. 1200 species, is the largest genus of Ericaceae (Chamberlain et al. 1996; MacKay and Gardiner 2017). This genus is widely distributed in Asia, Europe and North America, of which the great majority (ca. 900) occurs in China and the Malaysian archipelago, the centres of diversity being in the Himalayas and South East Asia (Fang et al. 2005; Brown et al. 2006; Gibbs et al. 2011; Liu et al. 2020). When we examined the type specimens of Rhododendron from Guizhou Province, China, R. leishanicum W. P. Fang et S. S. Chang ex D. F. Chamb. and R. oligocarpum W. P. Fang et S. S. Chang were found to be morphologically very similar and identified as very confusing in terms of leaf, flower, and fruit characters.

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 (Types: HGAS0088928, IBSC0481928, PE01297915, PE01297916), Z. S. Zhang 58 (HGAS007915), T. H. Tu 31739 (SZ0036179), from Fanjing Mountain; Austro-Guizhou Exped 1411 (PE00312607, PE00313389, KUN540382), from Leigong Mountain and G. Z. Li 6211 & 11277 (IBK00187538, IBK00187539 & IBK00187541, IBK00187559), 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). However, the relationship between R. oligocarpum and R. leishanicum was not mentioned by Fang when he described R. leishanicum as a new species again in the publication in 1983.

Figure 1. 

Rhododendron leishanicum and R. oligocarpum A isotype of R. leishanicum B holotype of R. oligocarpum C, D paratype from Leigong Mountain and Maoer Mountain of R. oligocarpum, respectively.

According to critical examination of the type specimens and morphological comparisons of R. leishanicum and R. oligocarpum, we found that both species have setose young branches and petioles, with small apiculate leathery leaves, racemose-umbellate inflorescences, corolla campanulate, with deep purple basal spots, pedicel, ovary and filament with identical indumentum (Fig. 2). It is worth noting that during our field surveys of populations of these two species, we observed a certain difference in colour of the corolla between the Guangxi population of R. oligocarpum and those in Guizhou. However, variation in corolla colour is known to occur within species of the genus Rhododendron (Jin 2006; Zhou 2008); hence, the differences in corolla colour between them fall within a normal range of variation. Therefore, we place R. oligocarpum in synonymy with R. leishanicum according to ICN rules (Turland et al. 2018).

Figure 2. 

Comparison of Rhododendron leishanicum and R. oligocarpum A, D, G, J, M R. leishanicum from Leigong mountain B, E, H, K, N R. oligocarpum from Fanjing mountain C, F, I, L, O R. oligocarpum from Maoer mountain A–C branchlets with flowers D–F adaxial and abaxial surface of leaf G–I corolla with deep purple basal spots J–L pedicel, Calyx, ovary and style indumentum M–O stamens side view.

Based on the setose branchlets and petioles, the small apiculate leaves, the campanulate corolla and the glabrous style, we suggest placing R. leishanicum in the Subsection Maculifera.

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 digitised specimens.