Haplodontiumaltunense (Bryaceae, Bryopsida), a new moss species from Northwest China

Abstract Haplodontiumaltunense X.R.Wang & S.Mamtimin, a new moss species of the family Bryaceae from Xinjiang Uygur Autonomous Region, China is described and illustrated. Genetic analysis based on ITS sequences shows that this species is a member of the Bryaceae and in the same clade as Anomobryum. Particularly distinctive features of the new species include: double peristome; the exostome has raised and membranous chomata with united lamellae between two teeth proximally; the endostome is poorly developed and all the endostomial material tightly adherent to the exostome.


Introduction
Haplodontium Hampe, classified in the family Bryaceae, has been confused with the genus Mielichhoferia Hornsch. Shaw and Crum (1984) transferred all species in the genus to Mielichhoferia because of the similar peristome. Genetic research (Cox et al. 2000;Goffinet et al. 2001;Pedersen et al. 2003Pedersen et al. , 2007Holyoak and Pedersen 2007) has clearly shown that some species originally in Haplodontium are nested within Bryaceae. Spence (2005) resurrected the genus Haplodontium and transferred two North American species of Mielichhoferia to Haplodontium. In addition, the genus Mielichhoferia has been accommodated in the family Mielichhoferiaceae (Shaw 2009). Pedersen et al. (2007) showed that Haplodontium, Acidodontium Schwägr. and Anomobryum Schimp. are sister taxa and Haplodontium should be included in the family Bryaceae.

Morphological observations
Microscopic examination was carried out using traditional methods. The collections of Haplodontium and relevant species of Bryaceae in the herbarium of Hebei Normal University (HBNU), Institute of Applied Ecology, Chinese Academy of Sciences (IFP), Kunming Institute of Botany, Chinese Academy of Sciences (KUN), Institute of Botany, the Chinese Academy of Sciences (PE) and Xinjiang University (XJU) were examined.
Authors observed the plants under the dissecting microscope and examined the leaves, capsules and peristome under the compound light microscope and scanning electron microscope. Light micrographs were photographed using a Nikon E-800 microscope with a Nikon DXM1200F digital camera. The peristome and spores were mounted on double sided sticky tape on aluminium stubs, gold-coated and viewed using a Hitachi S-4800 field emission SEM. All line drawings were made using the drawing tube attachments of these optical microscopes.

Phylogenetic analyses
Twenty-one samples were used for the analyses (Table 1). To evaluate the systematic position of Haplodontium altunense, 20 representatives of allied genera in the family Bryaceae, including Anomobryum, Bryum, Gemmabryum, Plagiobryum and Ptychostomum, were also sampled as part of the ingroup (Cox et al. 2000;Goffinet et al. 2001;Pedersen et al. 2003Pedersen et al. , 2007Kato et al. 2013). Bryum argenteum was selected as an outgroup. In addition to 10 sequences from GenBank, 11 sequences newly produced for the present study were included.
Genomic DNA was extracted from freshly collected and silica gel-dried plants using a Plant Genomic DNA Kit (TIANGEN Biotech (Beijing) Co., Ltd.) according to the manufacturer's protocol. One nuclear marker ITS was chosen. The following primers were used to amplify the marker: '18SF' and '26SR' for the ITS region, or sometimes '18SF' and '5.8SR' for ITS1, and '5.8SF' and '26SR' for ITS2 (Hartmann et al. 2006). PCR cycles used an initial denaturation step of 3 minutes at 95 °C, followed by 35 cycles of 30 seconds at 95 °C, 30 seconds at 50 °C, 90 seconds at 72 °C, and a final elongation of 5 minutes at 72 °C. PCR products were purified with a Gel Extraction Kit (Cwbio, Shanghai, China) following the instruction manual. These purified PCR products were sequenced by Life Technologies Inc., China (http://www.lifetechnologies.com).
Sequence chromatograms were compiled using SeqMan II (DNASTAR Inc., Madison, WI, USA) and then aligned manually in PhyDE 0.9971 ). Regions of partially incomplete data at the beginnings and ends of sequences were identified and excluded from subsequent analyses. Gaps were treated as missing data. The aligned ITS dataset was composed of 1213 bp.
The maximum likelihood (ML) method was performed using RAxML v.8.2.12 on the CIPRES Science Gateway (http://www.phylo.org/), and inferred under the default settings (Stamatakis 2014). The fast bootstrap option was used with 1000 replicates. TreeGraph 2 (Stöver and Müller 2010) was used to summarize the topologies and support values from the analyses.  Diagnosis. Particularly distinctive features of the new species including: double peristome; the exostome has raised and membranous chomata with united lamellae between two teeth proximally; the endostome is poorly developed and all the endostomial material tightly adherent to the exostome. Description. Plants small, soft and dull, brown-green. Stems short, 2.5-6 mm high, weakly julaceous, branched, circular or pentagonal circular in transverse section with small and thick-walled peripheral cells surrounding 2-3 layers gradually larger and thin-walled cortical cells, central strand weakly developed. Leaves imbricate when dry, erect when moist, enlarged towards stem apex, ovate to broadly ovate, concave, 0.5-1.1×0.3-0.7 mm; base not decurrent; margins plane or recurved medially, 1-stratose, limbidium absent, smooth or finely serrulate distally; apex broadly acute; costae not reaching apex, guide cells weakly developed, 2-4 in one layer in costal transverse section, ventral and dorsal stereid bands present; alar cells not differentiated from juxtacostal cells; laminal cells lax; distal laminal cells rhomboidal, 30-44×11-21 μm, with slightly thickened walls; medial laminal cells long rhomboidal to rectangular, 37-69×12-20 μm, somewhat narrower in 2 or 3 rows toward the margins but not forming a distinct border; proximal laminal cells long rectangular, 37-56×20-28 μm. Dioicous(?). Perigonia not seen. Perichaetia at the end of short, inconspicuous stems, appearing laterally because of well-developed innovations; perichaetial leaves larger than vegetative leaves. Setae single, light brown, 15-19 mm long. Capsules nutant and symmetric, reddish brown, obovoid, 1.5-2 mm, neck short and indistinct, mouth small, stomata abundant in the neck, superficial; opercula long-conic with short rostrate; annulus present, consisting of two rows of cells, revoluble and cells with slit-like lumen; peristome double, exostome inserted below the mouth, teeth lanceolate, redbrown and pored, raised and membranous chomata with united lamellae between two teeth proximally, pale yellow to hyaline and largely papillose along horizontal and median vertical lines distally; endostome poorly developed, basal membrane smooth, segments and cilia rudimentary, all the endostomial material strongly adhere to the exostome. Spores spherical, 20-22 μm in diameter, minutely papillose.

Taxonomic treatment
Etymology. The specific epithet altunense refers to the type locality in Altun Mountain National Nature Reserve in the Northwestern China.
Distribution and habitat. China (Xinjiang). Only known from the type locality, on soil substrates at 4290 m in the Altun Mountain National Nature Reserve. The population grows in a dry, cold, and windy habitat with intense evaporation. The companion species include some xerophytic mosses of the family Pottiaceae.

Discussion
Pending a careful examination of Bryaceae in the Altun Mountains, we discovered an unusual collection with distinctive morphological features of the peristome: endostome poorly developed and strongly adherent to the exostome. We thought this collection could belong to the genus Synthetodontium Cardot at first sight based on its fused peristome. Phylogenetic analysis showed that this collection was nested into Bryaceae clade. It is genetically distinct from the closely related Anomobryum group (Fig. 4). Further examination revealed that it has morphological characters of Haplodontium such as stems nearly julaceous, leaf margins entire, distal and medial laminal cells laxly rhomboidal to rectangular. However, the collection is distinguished from the other previously recognized species in the region by its double peristome, and raised and membranous chomata with united lamellae between two exostome teeth proximally. We thus describe it as a new species of the genus Haplodontium. The gametophytes of Haplodontium species are similar to those of Plagiobryum and Plagiobryoides J.R.Spence (Spence 2015). Genetic research has shown that the type species of Haplodontium is closely related to Acidodontium and Anomobryum (Cox and Hedderson 2003;Pedersen et al. 2007). Peristome reduction is common and complex in Haplodontium, from double to single to absent (Spence 2005).
The gametophyte characters of Haplodontium altunense are similar to Plagiobryoides brachyneura (Kindberg) J.R.Spence (Spence 2015). At the same time, both species have double, reduced and fused peristome. In P. brachyneura, setae are red-brown and 5-15 mm long, capsules are inclined to nutant, elongate-pyriform and 2-4 mm long with elongateneck, opercula are weakly convex, exostome teeth are short and irregular in shape. However, those characters of H. altunense are as follows: setae are light brown and 15-19 mm long, capsules are nutant, pyriform to obovoid and 1.5-2 mm long with indistinct short-neck, opercula are long-conic with short rostrate, exostome teeth are regular long lanceolate. Haplodontium altunense is also similar to Ptychostomum pendulum Hornschuch (Spence 2015) (≡Bryum algovicum Sendtner ex Müller Hal. (Li 2006;Zhang et al. 2007) in that the endostome adheres to the exostome teeth. While the former species differ from the latter one in length of stems (2.5-6 mm vs. 5-20 mm), leaf apex (broadly acute or obtuse vs. acuminate), leaf margin (indistinct bordered vs. strong limbidium), costae (ending at or near the apex vs. long-excurrent in denticulate awn), exostome teeth (united at the base, large papillose above vs. separate, smooth above), endostome (segments reduced vs. segments with ovate perforations). Wang et al. (2017)