﻿Sinosasagracilis (Poaceae, Bambusoideae), a new combination supported by morphological and phylogenetic evidence

﻿Abstract The results of phylogenetic analysis, based on the whole chloroplast genome and morphological study support the transfer of a long ignored bamboo species, Sasagracilis, to the recently established genus, Sinosasa, in this study. Morphologically, this species differs from all the other known Sinosasa species by having very short (2–3 mm) foliage leaf inner ligules, which is unusual in this genus. A revised description of its morphology and colour photos are also provided.


Introduction
Sinosasa L.C.Chia ex N.H.Xia, Q.M. Qin & Y.H.Tong was recently segregated from Sasa Makino and Shibata (1901) to accommodate some species previously placed in Sasa subg. Sasa from China, based on morphological and phylogenetic evidence (Qin et al. 2021). This genus differs from Sasa in having raceme-like (vs. panicle-like) synflorescences, two to three (vs. four to ten) florets per spikelet with a rudimentary terminal floret, three (vs. six) stamens and two (vs. three) stigmas per floret, wavy (vs. usually flat) foliage leaf blades when dry and relatively long (> 1 cm) (vs. short) foliage leaf inner ligules (Qin et al. 2021). Up to now, Sinosasa contains seven species endemic to subtropical areas of China and usually found growing along the river valley or in moist areas under evergreen broad-leaved forests at elevations of 700-1200 m (Qin et al. 2021).
Sasa gracilis B.M. Yang (1990) was described based on the only collection B. M. Yang 06774 from Shangmuyuan, Jiangyong County, Hunan Province, China. After its publication, it is only recognised in 'Bamboos of Hunan' (Yang 1993), edited by the author of this name, 'Iconographia Bambusoidearum Sinicarum' (Yi et al. 2008) and its English version 'Illustrated Flora of Bambusoideae in China' (Shi et al. 2022). However, because of the narrow circulation of the publication Acta Scientiarum Naturalium Universtis Normalis Hunanensis (later the name was changed to Journal of Natural Science of Hunan Normal University) at that time in China (Deng and Xia 2014), this species was ignored by the widely distributed monographs, such as 'Flora Reipublicae Popularis Sinicae', 'Flora of China', 'World Checklist of Bamboos and Rattans' (Hu 1996;Wang and Stapleton 2006;Vorontsova et al. 2016), the well-known database GrassBase-The Online World Grass Flora (Clayton et al. 2016) and some important websites like http://www.ipni.org, http://www.tropicos.org and http://www.theplantlist.org. In the protologue, this species was described to possess a suite of vegetative characters, such as solitary branches at each branching node, strongly raised supranodal ridges and wavy foliage leaf blades when dry, which fit well with the circumscription of Sinosasa. However, this species has very short foliage leaf inner ligules that are only 2-3 mm long, while all hitherto known Sinosasa species typically have more than 1 cm long inner ligules. Therefore, the taxonomic position of Sasa gracilis needs a further study.

Materials and methods
The specimens of Sasa gracilis were collected from its type locality during a field trip in September 2022. Fresh foliage leaves were deposited in silica gel for DNA extraction. Type specimens of Sasa gracilis deposited in the Herbarium of Hunan Normal University (HNNU) were examined. Observations and measurements were taken using a magnifier and a ruler with a scale of 0.5 mm. Some minor characters like the indumentum were observed with a stereomicroscope (Mshot MZ101). The morphological terms follow McClure (1966) and Beentje (2016). Herbarium acronyms follow Thiers (2022, continuously updated).
To study the phylogenetic position of Sasa gracilis within the tribe Arundinarieae, the whole chloroplast genomes were used for building the phylogenetic tree. A total of 24 representatives belonging to all the five subtribes of the tribe Arundinarieae (Zhang et al. 2020a) were sampled and Bambusa multiplex (Lour.) Raeusch. ex Schult. f. from the tribe Bambuseae was used as outgroup. All the sampled taxa, as well as their voucher information and GenBank accession numbers, are listed in Table 1.   (Wick et al. 2015). Finally, the sequence editing was manually operated in Geneious v. 9.1.4 (Kearse et al. 2012) with the structure of LSC-IRa-SSC-IRb.

Phylogenetic analysis
All the whole chloroplast genomes were aligned with MAFFT v. 7.490 (Katoh and Standley 2013) and combined as a data matrix. Phylogenetic analyses were conducted using Maximum Likelihood (ML) and Bayesian Inference (BI) implemented in the PhyloSuite v.1.2.2 platform (Zhang et al. 2020b). The best substitution model (K81 + GTR) for the combined data was determined using the Bayesian Information Criterion (BIC) in ModelFinder (Kalyaanamoorthy et al. 2017). A standard Maximum Likelihood tree search was performed using IQ-TREE v.1.6.8 (Nguyen et al. 2015). Nodal support (bootstrap support; BS) was assessed using 1000 standard bootstrap replicates. variable sites (2.56%), including 773 parsimony informative sites (0.54%) and 2,915 singleton variable sites (2.02%). The phylogenetic trees, generated by the ML and BI methods, were generally consistent in topology, so only the ML tree was shown with nodal support values from both methods labelled on each node (Fig. 1). As shown in the phylogenetic tree, Sasa gracilis is distantly related to Sasa veitchii Rehder (= Sasa albomarginata (Miq.) Makino & Shibata, the type of Sasa), but forms a monophyletic clade with three Sinosasa species with strong nodal support (BS = 100% and PP = 1.00).