Styrax hwangiae M.Tang & W.B.Xu, 2021

Xu, Wei-Bin, Yang, Ping, Huang, Yu-Song, Zhang, Rui & Tang, Ming, 2021, Styrax hwangiae (Styracaceae), a new species endemic to limestone areas of Guangxi, China, Phytotaxa 478 (1), pp. 171-178 : 172-176

Styrax hwangiae M.Tang & W.B.Xu , sp. nov. ( Figs. 1–3 ).

Type:— CHINA. Guangxi: Jingxi County, Daxing Village, Bangliang National Nature Reserve , limestone slope, broad-leaved forests, 700–800 m, 13 April 2020, P . Yang et al. BL448 (holotype IBK!; isotypes IBK!, JXAU!) .

Diagnosis:—S tyrax hwangiae is similar to S. rugosus but differs by its longer petiole, paniculate or racemose inflorescence with more flowers, calyx abaxially tissue extend outward into many spires covered by many trichomes, flexuous longer filaments, and larger fruits with thicker pericarp.

Evergreen shrubs or small trees, 2–14 m tall. Young branchlets yellowish brown-stellate-tomentose, older branchlets light black and glabrescent. Leaves alternate. Petiole 3–7 mm long, densely brown-stellate- tomentose. Leaf blades ovate-oblong or ovate, 3–15 × 2.0– 6.4 cm, coriaceous, base broadly or narrowly cuneate, slightly oblique, margin slightly undulate and revolute, apex acute or acuminate, mucronate; adaxially rugose and sparsely covered with simple black stellate trichomes, sometimes subglabrous when old, abaxially greyish white-stellate-tomentose; secondary veins 4–6 on each side of midvein, tertiary veins parallel, secondary and tertiary veins adaxially sunken, abaxially raised. Fertile shoots (3–)6–12(–17)-flowered, (4–)5–10(–12) cm long. Inflorescences usually paniculate, rarely racemose, rachis yellowish green-stellate-tomentose intermixed with sparsely stalked trichomes; bracteoles positioned at various places along pedicel or at base of calyx, linear, 3–6(–10) mm long, densely grey-stellate- tomentose, intermixed with stalked trichomes. Pedicel 5–15 mm long, stellate-tomentose. Flowers 1.5–2.0 cm long. Calyx hemispheric, 7–10 × 7–12 mm, grey-stellate- tomentose throughout, calyx tissue extend outward into many spires covered by many trichomes; margin irregularly dentate, teeth unequal, 2–5 mm long, broadly deltoid, obtuse, densely stellatetomentose, sometimes with 1 or 2 acute apexes. Corolla white, widely campanulate, 1.2–1.5 × 1.4–2.3 cm, tube 3–5 mm long, lobes 5, elliptic- obovate, 1.0–1.5 × 0.6–1.1 cm, densely pale stellate-pubescent both sides, apex sharply acute. Stamens 10; filaments 11–12 mm long, flexuous at right angles at midpoint, densely white-stellate-tomentose, becoming glabrous distally; anthers connivent, awl-shaped, ca. 0.7 mm long, connectives extending beyond thecae, thecae densely stellate-pubescent. Style densely white-stellate-villous; ovary ovoid, apical portion pubescence. Fruit dehiscent by 2 or 3 valves from the base, ovoid, 1.3–1.6 × 0.8–1.1 cm, apex rounded or apiculate; pericarp dry, 0.5–1 mm thick, outside densely whitish stellate-tomentose, inside glabrous or sparsely grey-pubescent. Seeds brown, ovoid, sparsely or densely appressed-stellate-pubescent or lepidote.

Distribution and Habitat: — Styrax hwangiae is endemic to southwestern Guangxi, China ( Fig. 4 ). It grows sporadically with other hardwoods in limestone areas at elevations of 300– 900 m.

Phenology: —Flowering April to May; fruiting August to October.

Etymology: —The species is named in honor of Professor Shu-Mei Hwang (Ȓ淑ẍ) from South China Botanical Garden, Chinese Academy of Sciences, who made outstanding contributions to the taxonomy of Styracaceae from China. Hwang was apparently the first to realize that Styrax hwangiae probably represents an undescribed species and provided the nude name ‘ Styrax longzhonica S.M.Hwang’ on the annotation labels of the specimens of C. C. Li 3223 (IBK) and S. H. Chun 13215 (IBK), both were collected from Longjin (= Longzhou) County in Guangxi. Hence we propose the Chinese name ‘淑ẍḙ息ḡ (shu mei an xi xiang)’.

IUCN Red List Category: — Styrax hwangiae is a narrowly distributed species with only six populations known, four in Jingxi County and two in Longzhou County. According to our observation, the populations in Jingxi County comprise no more than 50 plants. Moreover, the labels of the specimens collected from Longzhou County were stated “not common”, which suggests that the number of individuals in the Longzhou populations might also be very low. Considering the new species may be at risk of being cut down in the future because its distribution is too adjacent to the villages, we recommend that S. hwangiae be categorized as EN (endangered) under criteria B and D following IUCN Red List categories ( IUCN Standards and Petitions Subcommittee 2019).

Additional specimens examined (paratypes): — CHINA. Guangxi: Jingxi County, Bangliang forests, 29 September 2007, W. B . Xu & Y. Y . Liang B0080 ( IBK!), 28 April 2008, W. B . Xu & Y . X. Zhu B0549 ( IBK!), 7 May 2008, W. B . Xu & Y . X. Zhu B0669 ( IBK!), Bangliang National Nature Reserve , 10 September 2010, Y. S . Huang & B . Pan LYJX0168 ( GXMG!, IBK!), Bangliang Village , 20 April 2020, P . Yang et al. BL587 ( IBK!), Daxing Village , 15 April 2020, P . Yang et al. BL492 ( IBK!), Erlang Village , 18 April 2020, P . Yang et al. BL546 ( IBK!), Luoguo Village , 26 September 2010, Y. S . Huang & L . Wu LYJX0739 ( GXMG!, IBK!); Longzhou County, Paotai Mountain , 3 October 1956, C. C . Li 3223 ( IBK!, IBSC!), Qingshan Village , 12 July 1957, S. H . Chun 13215 ( IBK!, IBSC!) .

Discussion: — Styrax hwangiae is morphologically similar to S. rugosus by its rugose leaves, and somewhat by the shape of its flowers and fruits, but differs by its longer petiole (3–7 vs 2–3 mm), leaf blade with slightly undulate and revolute margin (vs. serrate or apically dentate, margin not revolute), the lager (7–10 × 7–12 vs. 4.5–5.0 × 3.5–5.0 mm) calyx with its abaxial tissue extending outward into many spires covered by many trichomes and deltoid calyx lobes (vs. short white 2- or 3-armed or stellate trichomes), the longer filaments (11–12 mm vs. 7–8 mm) flexuous at right angles at the upper part (vs. straight), larger fruits (1.3–1.6 × 0.8–1.1 cm vs. 0.7–0.9 × 0.5–0.6 cm), thicker pericarp (0.5–1 mm vs. 0.2–0.3 mm) and seed coat morphology (appressed-stellate-pubescent or lepidote vs. smooth, glabrous). Styrax hwangiae is also similar to S. tonkinensis (Pierre 1892: 151) Craib ex Hartw. (1913: 698) in the habit and leaf shape, but differs by its thickly leathery and rugose leaf blades, larger hemispheric calyx, calyx tissue extend outward into many spires covered by many trichomes, and shorter fertile shoots. The morphological differences of these three species are summarized in Table 1. Due to S. hwangiae ’s paniculate or racemose inflorescences and imbricate corolla, it is no doubt belongs to S. ser. Cyrta according to Fritsch (1999), despite its evergreen habit that differs from other species of the series.

Notes: The morphological comparisons of Styrax rugosus and S. tonkinensis are based on specimens examined and the descriptions in Huang et al. (2003).

Figures

FIGURE 1. Holotype sheet of Styrax hwangiae (Jingxi, Guangxi, China, P. Yang et al. BL448 (IBK)).

FIGURE 2. Specimens of Styrax hwangiae. A. Jingxi County, Guangxi Province, China, P. Yang et al. BL448 (isotype, IBK). B. Jingxi County, Guangxi Province, China, P. Yang et al. BL587 (paratype, IBK). C. Jingxi County, Guangxi Province, China, W. B. Xu & Y. Y. Liang B0080 (paratype, IBK). D. Jingxi County, Guangxi Province, China, Y. S. Huang & L. Wu LYJX0739 (paratype, IBK).

FIGURE 3. Styrax hwangiae (Jingxi, Guangxi, China) A. Habitat and habit. B. Inflorescence. C. Leaf blades in adaxial (left) and abaxial (right) view. D. Flower (apical view). E. Flower (lateral view). F. Sepals (adaxial view of four sepals pulled apart at the lobe margins of one calyx). G. Sepals (basal view of sepals pulled apart at the lobe margins of one calyx, noting the calyx tissue extend outward into many spires covered by many trichomes). H. Opened corolla (abaxial view). I. Opened corolla plus androecium, ventral view (note flexuous filaments at right angles at the upper part). J. Five stamens (abaxial view). K. Ovary apex and style. L. Fruit (persistent calyx excluded). M. Seed.

FIGURE 4. Distribution map of Styrax hwangiae (★).