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Dendrocalamus menghanensis (Poaceae, Bambusoideae), a new woody bamboo from Yunnan, China

Abstract Dendrocalamus menghanensis P.Y.Wang & D.Z.Li, a new species of woody bamboos endemic to south Yunnan, China, is described and illustrated. The new species is morphologically similar to D. semiscandens and D. birmanicus but differs in having a reflexed culm sheath blade, 10 mm high culm sheath ligule, 1 mm high leaf sheath ligule, 4 florets and 1 glume.


Introduction
The genus Dendrocalamus was described by Nees von Esenbeck (1835) and currently comprises of more than 50 species in tropical and subtropical regions of Asia (Ohrnberger 1999, Bamboo Phylogeny Group 2012. Several new species in this genus have been continuously described in recent years (Yang et al. 2016, Wang et al. 2016, Nguyen et al. 2017a, 2017b. There are about 30 species of Dendrocalamus distributed in China (including new species described in recent years) (Li et al. 2006). It is a typical paleotropical woody bamboo genus belonging to the subtribe Bambusinae Presl (1830) of tribe Bambuseae Kunth ex Dumortier (1829). Within this subtribe, the three major genera are Bambusa (von Schreber 1789), Dendrocalamus and Gigantochloa Kurz ex Munro (1868). They formed a clade known as the BDG complex (Goh et al. 2010(Goh et al. , 2013, also named "core Bambusinae", but the long-standing problems for taxonomic delimitation and evolutionary relationships within the BDG complex have not been satisfactorily resolved (Goh 2012, Chokthaweepanich 2014, Zhou et al. 2017.
Most of the species of Dendrocalamus can be recognised by their thick-walled culms, swollen nodes reflexed culm sheath blade and aerial roots at the lower nodes. The species usually have white, blackish or light-brown hairs on the culm sheaths (Dransfield 1980). Compared to Dendrocalamus, it is easy to classify the Bambusa species by the erect culm sheath blade and conspicuous auricles and Gigantochloa by connate filaments. While checking the bamboos cultivated in Xishuangbanna Tropical Botanical Garden (XTBG), Chinese Academy of Sciences (CAS), we discovered an extraordinary Dendrocalamus species. The floret of this species has no lodicule, one plumose stigma, six stamens and completely separate filaments, indicating that it belongs to Dendrocalamus rather than to Gigantochloa or Bambusa (Li and Hsueh 1988a, 1988b, Dransfield and Widjaja 1995, McClure 1966, Wong 1995, Li et al. 2006, Clayton et al. 2008, Sungkaew 2008. This new species resembles D. semiscandens (Li and Hsueh 1989) and D. birmanicus Camus (1932) in some morphological characters as discussed below (see Table 1). It was introduced in XTBG from Menghan Township, Jinghong, Yunnan, China in 1980.

Material and methods
All measurements of the new Dendrocalamus species were taken from dried herbarium specimens and living individuals at XTBG, Menglun, Mengla, Yunnan province. For morphological characterisation, vegetative parts of plant material were measured using the living plants and the reproductive parts were analysed under an automated digital microscope (ZEISS Smartzoom 5) linked with a computer in Xishuangbanna Station for Tropical Rainforest Ecosystem Studies of XTBG, CAS. The morphological terminology followed McClure (1966). Diagnosis. Dendrocalamus menghanensis is morphologically similar to D. semiscandens and D. birmanicus, but can be easily distinguished from them by having a reflexed culm sheath blade, 10 mm high culm sheath ligule, 1 mm high leaf sheath ligule, 4 florets and 1 glume.
Conservation status. As a great many forests have been destroyed by local people in the last 30 years, we did not find the new species at the locality where it was introduced. Further investigation is required to find more distribution localities and determine the conservation status of the new species. At present, we consider it as DD (Deficient Data) according to the IUCN parameters (IUCN 2012).

Discussion
Dendrocalamus menghanensis is morphologically similar to D. semiscandens and D. birmanicus. However, the new species differs from them by having a reflexed culm sheath blade, 10 mm high culm sheath ligule, 1 mm high leaf sheath ligule, 4 florets and 1 glume. The major differences amongst these species are listed in Table 1. This new species is only found in Xishuangbanna which is located in one of the world's biodiversity hotspots (Indo-Burma) (Myers et al. 2000). Many forests have been destroyed because of the plantation of rubber trees in this region in the past 30 years. Many species may become extinct before we know that they exist in Xishuangbanna. More field investigations need to be conducted in this region in future.