Gelidocalamus xunwuensis W.G.Zhang & G.Y.Yang, a new species collected from Xunwu County of Jiangxi Province in China, is described and illustrated. The new species is similar to G. stellatus in the habit, but differs by internodes sparsely hairy with granuliferous warts, culm sheath stiffly hairy, culm sheath blade broadly lanceolate to narrowly triangular, each node with a ring of appressed trichomes below, foliage leaves broadly lanceolate to narrowly oblong, and new shoots occurring in late October.

Arundinarieae , Bambusoideae , bamboo, leaf epidermis, SEM, taxonomy

The genus Gelidocalamus Wen (1982: 21) includes ca. 9-13 species in the tribe Arundinarieae (Poaceae: Bambusoideae) and is endemic to China. This genus is characterized by leptomorph rhizomes, several branches per node, leaves usually solitary on each ultimate branch, semelauctant inflorescence, three stamens, and with new shoots occurring in the autumn to winter seasons (Wen 1982, Geng and Wang 1996, Li et al. 2006, Yi et al. 2008, Soreng et al. 2015, Liu et al. 2017).

Most species of Gelidocalamus are restricted to southern China in Hunan, Jiangxi, Zhejiang, Fujian, Taiwan, Guangdong, Guangxi, Yunnan, and Guizhou Provinces, and distributed at elevations of 200–1200 m, along ravines and under evergreen broad-leaved forests (Li et al. 2016). However, within the past 30 years, most newly discovered species, e.g. Gelidocalamus annulatus T. H. Wen, G. longiinternodus T. H. Wen & S. C. Chen, G. multifolius B. M. Yang and G. dongdingensis C. F. Huang & C. D. Dai, are known only from their type locations suggesting that the diversity and distribution of Gelidocalamus species is in need of further study.

During a botanical expedition in central and southern China in 2014, a distinctive “Gelidocalamus-like” collection with many branches per node and leaf solitary on each ultimate branch was found from Xunwu County. Xunwu County (24°30'40"–25°12'10"N, 115°21'22"–115°54'25"E) is a hot and humid region in the southeastern corner of Jiangxi Province, located at the junction of Wuyi Mountain and Jiulian Mountain, and has a subtropical climate with abundant monsoon rainfall. It is also a minor centre of plant endemism in China and especially exhibits high richness in palaeo-endemic species (Jordi et al. 2011). Twenty-six endemic species and 11 new species have been discovered in this region in recent years (Ji 2007, Ji et al. 2010).

To investigate this collection, we made a complete morphological characterization, including description, illustrations, taxonomic comments, and scanning electron microscope (SEM) images of the abaxial leaf epidermis. This collection has the typical characteristics of Gelidocalamus with leptomorph rhizomes, several branches per node and leaves usually solitary on each ultimate branch. It can be readily distinguished from other Gelidocalamus species by its internodes being sparsely hairy with granuliferous warts, culm sheath stiffly hairy, and foliage leaves broadly lanceolate to narrowly oblong. By all the evidence obtained, we believe that this collection is a new species and herein described and illustrated.

From Jul. 2014 to Nov. 2016, mature leaves were collected from individuals of the type localities (the Xunwu population – the Guizhumao of Xunwu in Jiangxi, Gelidocalamus stellatus T. H. Wen – the Xiazhuang of Jinggang Mountain in Jiangxi, G. tessellatus T. H. Wen & C. C. Chang – the Maolan of Libo in Guizhou, G. dongdingensis C. F. Huang & C. D. Dai – the Dongding Mountain of Longyan in Fujian, respectively) and immediately fixed in FAA solution. Leaves were cleaned by ultrasonic wave with ultrapure water, dried at room temperature, and mounted on stubs. After gold sputtering, the samples were photographed using the scanning electron microscope Hitachi S-4800. Terminology for the epidermis appendages follows Ellis (1979), Wu et al. (2014), and Zhang et al. (2014). Voucher specimens were deposited in the herbarium of the College of Forestry, Jiangxi Agricultural University, China (JXAU). Morphological traits, including habit and new shoot, culm and culm sheath, branch and leaf, were described with both fresh and exsiccated specimens.

The Xunwu population plants are most similar to G. stellatus in the habit and branching pattern. However, they differ from the latter by the following characters: culms sparsely hairy (vs. glabrous) with granuliferous warts (vs. smooth), culm leaf sheath densely hispidulous (vs. hairless), each node with a ring of fulvous appressed trichomes below (vs. white appressed trichomes), foliage leaves oblong (vs. lanceolate) and new shoot in late Oct. (vs. early Sep.) (Table 1 and Fig. 1).

Leaf epidermis characters of the Xunwu population plants are almost identical to that of Gelidocalamus stellatus Wen (1982: 22) and G. tessellatus T. H. Wen & C. C. Chang (1982: 24) (Fig. 2A–C). Each stomatal apparatus (usually 3 rows between the veins) is surrounded by 8–10 short papillae, but covered with dense wax. The saddle-shaped silica bodies on the veins can be clearly identified, but the long cells and short cells cannot be distinguished. Microhairs are gracile, composed of two cells with the apical cell withered, and mostly occur on the intercostal regions of the abaxial leaf epidermis.

On the contrary, Gelidocalamus dongdingensis, a species collected from the adjacent area of Xunwu County, Longyan of Fujian (about 200 km), has obviously different characters of leaf epidermis (Fig. 2D). Each stomatal apparatus (usually 8–10 rows between the veins) is nearly invisible, overarched by 14–20 long papillae. The saddle-shaped silica bodies on the veins can be also clearly identified. However, there are three types of trichomes (i.e. macrohairs, microhairs and prickles) on the abaxial leaf epidermis. Except microhairs, macrohairs can be visualized with the naked eye and can be used to discriminate from the Xunwu population plants, while prickles are short and relatively stiff with sharp apices, located at the intercostal regions.

Figure 1. 

Comparison of morphological characters between plants from Xunwu (A–I) and Gelidocalamus stellatus (J–R). A–D, J–M culm and node E–G, N–P culm leaf sheath H, Q branch sheath I, R foliage leaf. Scale bars: 3 mm (A–C, E, J–L, N), 1 mm (D, F–H, M, O–Q), 2 cm (I, R).

Figure 2. 

SEM images of the abaxial leaf epidermis. A Xunwu plants (Xunwu, Jiangxi, China) B Gelidocalamus stellatus (Jinggang Mountain, Jiangxi, China). C Gelidocalamus tessellatus (Libo, Guizhou, China) D Gelidocalamus dongdingensis (Longyan, Fujian, China).

Recently, phylogenetic studies have indicated that Gelidocalamus is polyphyletic (Zeng et al. 2010, Zhang et al. 2012). Four species (G. tessellatus, G. rutilans T. H. Wen and two unnamed species) were examined by Zeng et al. (2010) and were found to be widely divergent. However, few species have been examined molecularly and more extensive sampling within Gelidocalamus is necessary. Similarly, studies of leaf micromorphology show that there are various patterns of the papillae surrounding the stomata among species of Gelidocalamus (Wu et al. 2014, Zhang et al. 2014, Liu et al. 2017).

In contrast, previous studies have also shown that leaf epidermis characters are almost identical among the main taxa of Gelidocalamus, e.g. G. stellatus, G. tessellatus, G. annulatus, G. multifolius, G. latifolius T. H. Wen (1985: 53) (Wu et al. 2014, Zhang et al. 2014, Long et al. 2015). The stomatal apparatuses are embossed outwards and usually surrounded by ca. 6–10 short papillae, obviously distinguished from those of other taxa, such as G. subsolidus W. T. Lin & Z. J. Feng (1990 : 18), G. solidus C. D. Chu & C. S. Chao (1984:75), G. rutilans, G. monophyllus (Yi & B. M. Yang) B. M. Yang (1989: 338), G. kunishii (Hayata) P. C. Keng & T. H. Wen (1983: 20) and G. dongdingensis (Fig. 2D) (Wu et al. 2014, Zhang et al. 2014, Liu et al. 2017), indicating that the genus Gelidocalamus may be good after eliminating several taxa.

In the present study, the Xunwu population has the typical characteristics of Gelidocalamus, and can be readily distinguished from other Gelidocalamus species as observed above. Based on the unique morphological characters, and possibly the disjunct distribution of the new species, we believe that the Xunwu population represents a new species, and is herein described and illustrated.

Thanks go to Lin Shu-Wen and Pan Guo-Xin (Department of Forest Administration, Xunwu County) for their help during the field work, and to two anonymous reviewers for the helpful suggestions. This work was supported by National Natural Science Foundation of China (31500189 and 31260043), National Twelfth Five Year Plan for Science and Technology Support Project (2015BAD04B01) and 2011 Collaborative Innovation Center of Jiangxi Typical Trees Cultivation and Utilization.