Rhododendron yuanbaoshanense Y.H. Deng & Tao Ding, 2025

Deng, Yi-Hui, Pan, Bo, Ding, Tao, Liu, Hong, Qin, Xue-Lian, Huang, Zi-Xiong & Deng, Min- Min, 2025, Rhododendron yuanbaoshanense (Ericaceae), a new species from Guangxi, China, Phytotaxa 682 (2), pp. 179-184 : 179-183

Rhododendron yuanbaoshanense Y.H. Deng & Tao Ding , sp. nov. ( Figs. 1 & 2)

Diagnosis. The new species is most similar to Rhododendron yuefengense Li (1995: 293) in its funnelform-campanulate to campanulate corolla and pink to pale pinkish-purple color, outside sparsely glandular, glandular calyx, and glandular style, but differs in having broadly ovate to orbicular (vs. sub-round or heart-shaped) and larger leaf blades (7–15.5×5.2– 12. 8 cm vs. 5.5–9.5× 4–8 cm) with a cordate-auriculate (vs. sub-rounded to shallowly cordate) base, longer (3–8 cm vs. 1.5–2.5 cm) and cylindric (vs. cylindric, flattened above) petioles, and glandular or densely glandular inflorescence rachises (vs. sparsely glandular).

Type. CHINA. Guangxi: Rongshui County, Antai Community, Xiaosang Village, 109°8′27.15″E, 25°24′6.94″N, alt. ca. 1380 m, on steep slopes, 9 May 2024 (flowering), T. Ding, B. Pan & Y. H. Deng DT20240014 (holotype: IBK!).

FIGURE 2. Rhododendron yuanbaoshanense . ( A, D, G, I, K – M), R. yuefengense ( B, E, H, J) and R. orbiculare ( C & F). A & B & C. Flowering branch; D & E & F. Leafy branches; G & H. Adaxial and abaxial surfaces of leaves; I & J. Inflorescence rachises and pedicels; K. Dissection of flower, showing corolla, pistil and stamens; L. Transection of ovary, showing glands on ovary, calyx and pedicels; M. Capsules; N. Habit; O. Habitat.

Shrub evergreen, 1–2 m tall. Bark brown. Young branches yellowish-green, glandular; old branches brown. Leaves thickly leathery, broadly ovate to orbicular, 7–15.5× 5.2–12.8 cm, apex rounded, cuspidate, base auriculate-cordate, dark green above, pale green to pale white below, midrib slightly depressed above, raised below, lateral veins 8–13 pairs, reticulate veins slightly raised on both surfaces; petiole cylindric, 3–8 cm long, pale green, sometimes purplish red, sparsely glandular when young and nearly smooth when old. Racemose umbels terminal, lax, 8–17-flowered; rachis 5.5–9.5 cm long, glandular or densely glandular; pedicels 2.4–4.6 cm long, yellowish-green, densely shortly stalked glandular; calyx small, yellowish-green, annular or 7-toothed, glandular; corolla funnelform-campanulate to campanulate, 3.5–5.7 cm long, pink to pale pinkish-purple, outside sparsely glandular, lobes 7, ovate-orbicular, 1.6–2 cm long, rounded at tip, not notched; stamens 14–15, unequal, 16–30 mm long, filaments white, glabrous, anthers long ellipsoid, brown, 3–4.5 mm long; ovary conical, light green, densely glandular, 10-loculed, styles 3.1–4 cm long, densely white glandular, stigmas yellowish-green, disk-shaped. Capsule oblong-ovate to oblong-elliptic, straight or slightly curved, 10–25× 6–10 mm, brown, ribbed and with persistent glands. Fl. April to May.

Phenology. Flowering from April to May, fruiting from May to September.

Etymology. The epithet of the new species is named after the type locality, Yuanbaoshan Mountain. Chinese name is yuán bǎo shān dù juān(pinyin).

Distribution and ecology. Currently, Rhododendron yuanbaoshanense is only distributed in its type location, Yuanbaoshan Mountain, Rongshui County, northern Guangxi, China, at elevations of 1200–1450 m. It grows in evergreen deciduous broad-leaved mixed forest. The main associated trees are Schima argentea E. Pritz. ( Theaceae ), Carpinus viminea Lindl. ( Betulaceae ) and Toxicodendron succedaneum (L.) Kuntze ( Anacardiaceae ), etc., shrubs are Erythroxylum sinense C. Y. Wu ( Erythroxylaceae ), Viburnum sympodiale Graebn. ( Viburnaceae ), Itea chinensis Hook. &Arn. ( Iteaceae ) and R. simsii Planch. ( Ericaceae ), etc., and herbs are Hosta ventricosa (Salisb.) Stearn ( Asparagaceae ), Tricyrtis macropoda Miq. ( Liliaceae ) and Ypsilandra thibetica Franch. ( Melanthiaceae ), etc.

Conservation status: R. yuanbaoshanense is currently only found in the Yuanbaoshan National Nature Reserve in Rongshui County, Guangxi, China. According to field investigation, only one population grows on steep slopes with a total number of ca. 80 individuals. In addition, a large number of tourists go to Yuanbaoshan National Nature Reserve in May every year to view the "Azalea" flower sea, which may threaten the habitat of the new species, resulting in population reduction. Thus, the conservation status is tentatively classified as Critically Endangered (CR) (B2ab (iii, v) + C2a (ii)) according to the IUCN Red List Categories and Criteria ( IUCN 2024). Therefore, it is imperative to implement in-situ or ex-situ conservation measures for its protection.

Similar species: Rhododendron yuanbaoshanense is most similar to R. yuefengense , which was described based on specimens collected from Mao’ershan Mountain of Guilin in northern Guangxi and also occurs in northern Guangxi. A detailed comparison of the two species refers to diagnosis part and Table 1. According to the latest taxonomic treatment, R. yuefengens e is considered as a variety of R. platypodum Diels (1900: 511) ( Geng 2014, Zhang et al. 2022). However, we do not agree this treatment. Rhododenron yuefengense has sub-round or heart-shaped leaves with cylindric petioles that are 1.5–2.5 cm long and 3–5 mm wide, and 2.5–3.5 cm long capsules, while R. platypodum has broadly elliptic or suborbicular leaves with flattened and winged petioles that are 1–2 cm long and 3–10 mm wide, and 1.5 cm long capsules. Therefore, R. yuefengense and R. platypodum are morphologically distinct. Rhododendron yuanbaoshanense is similar to R. platypodum in corolla shape, but is easily distinguished by leaf shape, leaf base shape, petiole length, petiole shape and flower color ( Table 1). Another species, R. orbiculare Decaisne (1877: 169) , occurred in western and southern Sichuan, China, has a similar leaf shape to R. yuanbaoshanense , but can be easily distinguished by flower shape, flower color, corolla, flower number per inflorescence, style and rachis length ( Table 1).

Figures

FIGURE 1. Rhododendron yuanbaoshanense Y.H. Deng & Tao Ding. A. Flowering branch; B. Inflorescence; C. Opened corolla; D. Pistil and calyx; E. Stamens; F. Leaf, adaxial surface; G. Leaf, abaxial surface.