Two new species of Fargesia (Poaceae, Bambusoideae) from southwestern China

Abstract Two new species of Fargesia, one from Xizang (Tibet) and one from Yunnan, China, are described and illustrated. Fargesia viridis D.Z. Li & X.Y. Ye is characterized by its densely white powder, nearly solid internodes, yellow setose sheath scar and culm sheaths, and 4–6 leaves of large size. Fargesia purpurea D.Z. Li & X.Y. Ye has thinner culms (0.5–1.4 cm in diameter), a ring of 4–5 mm tall brown setae below nodes, fewer branches, glabrous sheath scar and culm sheaths, differentiated from the related species.


Introduction
Tribe Arundinarieae, i.e. the temperate woody bamboos, is one of the three tribes of the subfamily Bambusoideae (Poaceae), containing approximately 581 species in 31 genera (Bamboo Phylogeny Group 2012; Clark et al. 2015;Clark and Oliveira 2018). These bamboos are distributed primarily in the temperate to subtropical zones of the Northern Hemisphere, with nearly 90% of species distributed in East Asia (Ohrnberger 1999;Li et al. 2006).
Among the 31 genera, Fargesia Franchet is the largest one, consisting of more than 90 species (Li et al. 2006;Yi et al. 2008), out of which, 85 species occur in China and 83 taxa are endemic to the country (Vorontsova et al. 2016). The Fargesia species are mainly distributed in temperate mountain areas (alt. 800-4300 m) of East Asia (Keng 1987;Yi 1988;Ohrnberger 1999;Li et al. 2006;Vorontsova et al. 2016). This group is especially common and diverse in the high elevation ecosystem of southwest China where they have undergone rapid diversification associated with the orogeny of the Hengduan mountains (Ye et al. 2019).
Fargesia is characterized by the presence of short-necked pachymorph rhizomes (usually < 20 cm), unicaespitose clumps, 7-15 branches at mid-culm nodes, semelauctant inflorescence, racemose to paniculate, compressed or open, with 3 stamens (Li et al. 2006). Although reproductive features are important for bamboo classification, vegetative morphological characters are usually used to distinguish species due to long flowering cycles (Janzen 1976;Zhang and Ren 2016). Based on morphological characters of buds and culm sheaths, Yi (1988) divided the genus Fargesia into two sections, F. sect. Ampullares Yi and F. sect. Fargesia (Keng and Wang 1996). The section Ampullares is distinguished by compound buds consisting of multiple distinct buds and deciduous culm sheaths. The section Fargesia is characterized by compound buds composed of several obscure buds and late deciduous or persistent culm sheaths, and contains four series, namely, ser. Murielae Yi, ser. Fargesia Yi, ser. Angustissimae Yi and ser. Yunnanenses Yi. The series Murielae has oblong or narrowly elliptical culm sheaths, with rounded apex, as wide as the base, while in the latter three series, the shape of culm sheaths is different and featured as narrowly triangular or narrowly orbiculartriangular, apex triangular or linear, much narrower than the base. Moreover, the texture and length of culm sheaths are varied in these three series. For example, the culm sheaths of ser. Fargesia and ser. Angustissimae are longer than internodes, but shorter or equal in ser. Yunnanenses. The culm sheaths of ser. Fargesia are apically leathery and narrowed for distal ca. 1/5 of length but apically thickly papery and narrowed for distal ca. 1/3-1/2 of length for species of ser. Angustissimae.
Although flowering is not frequent in this genus, it shows considerable diversity in vegetative morphology and many new species continue to be described (Yi 2000a, Yi 2000b, Yi 2000cYi et al. 2005Yi et al. , 2006Yi et al. 2007;Yi 2013a, Yang andYi 2013b) from southwest China. During floristic surveys of bamboos between 2015 and 2018, the authors collected vast specimens of Fargesia from southwest China. After scrutiny of the data available (Keng and Wang 1996;Li et al. 2006;Yi et al. 2008;Vorontsova et al. 2016), we found that several specimens could not be assigned to any described species. Here, we described two new species of Fargesia based on morphological comparison and the phylogenetic results (Ye et al. 2019).
Distribution and habitat. Fargesia viridis is only known from the type locality, the Dulongjiang Town. It occurs along the stream and grows as pure bamboo forest or under the evergreen broadleaved forest at an elevation of 2600-2800 m alt.
Phenology. New shoots July to August. Etymology. The specific epithet refers to the color of culm sheath and leaf sheath.   Notes. Morphological comparisons between Fargesia purpurea and the related species were provided in Table 2. Two species of this genus were distributed in the Zayu county, namely, F. zayuensis Yi and F. macclureana (Bor) Stapleton, with this new species being easily distinguished from them in this region by its glabrous culm sheath and abaxially densely white pubescent leaf blade.

Discussion
Both Fargesia viridis and F. purpurea have persistent culm sheaths and buds containing several obscure buds, making them belong to the section Fargesia. The shape of culm sheaths is different from these two species. F. viridis is characterized by narrowly rounded culm sheath, with apex nearly as wide as base, which is similar to the species of the series Murielae. F. purpurea is characterized by triangular culm sheaths, shorter than internodes, with apex narrower than base; these features are similar to those species of Fargesia is a polyphyletic genus and could be divided into three or four clades based on plastome sequences (Zhang et al. 2018;Zhou et al. 2019) and double-digested restriction enzyme-associated DNA sequencing (ddRAD-seq) data (Ye et al. 2019). F. viridis was classified as belonging to V-Fargesia4 clade based on the phylogenetic results of ddRAD-seq analyses (Ye et al. 2019), but no conclusion could be made for its position on the plastome phylogeny. Additionally, the phylogenetic relationship of F. purpurea in Fargesia has not been studied and that may be supplemented in the future.
Fargesia viridis (F. sp.2 in Fig. 2 of Ye et al. 2019) is closest to F. frigidis not only in morphology but also in phylogenetic relationships (Table 1, Ye et al. 2019), but the altitude distribution range of them are different. Moreover, F. viridis can be easily distinguished from F. frigidis by several morphologic characters, i.e. thinner culms, glabrous internodes, more leaves on ultimate branch. According to the identification keys, F. viridis is also similar to F. zayuensis and F. similaris; for example, they all have narrowly rounded culm sheath, with apex nearly as wide as the base, branch number usually above 5, auricles absent, glabrous leaf blade. However, a number of subtle features make F. viridis distinctive, such as internode nearly solid, densely white powdery culm, culm sheath persistent and densely yellow setose.
Fargesia purpurea resembles F. pauciflora and F. brevistipedis by its internode length, prominent sheath scar, culm sheath persistent, auricles and oral setae absent, and leaf blade abaxially pubescent, but differs in terms of the habitat, thinner culm, internode with a ring of 4-5 mm brown setulose, less branch number, glabrous culm sheath and sheath scar.
Mountains of Southwest China are the diversity center for Fargesia species; 80 out of 85 are distributed in this area and 73 of them are endemic. The two new species established here are also distributed in these mountains, indicating that the species diversity of Fargesia in this region may be beyond our knowledge. The species of Fargesia have an island-like distribution and allopatric speciation might have great impact on their diversity (Ye et al. 2019). However, the diversification of species could be caused by many reasons, such as heterogeneous environment, fluctuating climatic conditions, and adaptive evolution (Xing and Ree 2017;Ding et al. 2020). This genus with species distributed on a different elevation provides a case to disentangle the extrinsic and intrinsic factors that could promote species divergence. And research in this area may improve our ability to predict the evolutionary tendency and mitigate the threats posed by global warming to species distributed in the mountains of Southwest China.