﻿A new propaguliferous species of Pohlia (Mielichhoferiaceae, Bryopsida) from Tibet, China

﻿Abstract A new propaguliferous moss species, Pohliatibetana X.R.Wang & X.M.Shao (Mielichhoferiaceae), from Tibet, southwest China, is described. The new species differs most saliently from other species of Pohlia by its combination of slender plants, loosely attached leaves and axillary solitary, and dark red and flower-like gemmae. In this paper, the line drawings, photographs, habit of the new species are provided and a morphological comparison of it with the similar species is made.


Introduction
Asexual reproduction is a remarkable feature and widespread in bryophytes (Frey and Kürschner 2011). Asexual propagules play important roles when sexual reproduction is not attainable (Imura 1994) and can be produced under more stressful conditions and germinate more rapidly in contrast to spores (Newton and Mishler 1994). Vegetative diaspores may come from caducous fragmentation of gametophytic parts (leaves, leaf apices, shoots, branches and bulbils), specialized propagules (gemmae, protonemal brood cells and tubers) or clonal reproduction (Newton and Mishler 1994;Frey and Kürschner 2011).
A group of species in the genus Pohlia Hedwig (Mielichhoferiaceae Schimp.) produce specialized asexual propagules and the characters of propagule were used to distinguish various species (Cao and Zhao 2009;Liu et al. 2018). The habitat and the gametophyte characters of these species are very similar. Shaw made a taxonomic revision of the propaguliferous species of Pohlia in North America to better identify them (Shaw 1981a). In Czernyadjeva's (1999) study of propaguliferous Pohlia founded in Russia and adjacent regions, the distribution with maps and habitat preferences of nine species was discussed. A taxonomic and descriptive study of seven propaguliferous species with axillary gemmae of Pohlia in the Iberian Peninsula was made by Guerra (2007). In addition to providing the information on the habitat and distribution, Guerra also gave the photomicrographs of gemmae of each species. Suárez and Schiavone (2011a) meticulously compared the taxonomically important characters of American Pohlia species in habits and morphology of stems, leaves, perichaetial leaves, setae, stomas, peristome and annulus. They revised the propaguliferous species of Pohlia from Central and South America and presented the morphological illustrations and photomicrographs of six species with axillary gemmae and one with rhizoidal tubers (Suárez and Schiavone 2011a). Liu et al. (2018) presented the taxonomic study of ten species of Pohlia with axillary and rhizoidal propagules in China, including two new records: P. andalusica (Höhn.) Brotherus and P. andrewsii A.J. Shaw. with the photomicrographs of propagules and line drawings were provided. Wang et al. (2020) reported another newly recorded species with axillary gemmae to China from Tibet: Pohlia tundrae A. J. Shaw.
Recently, the authors revised the genus Pohlia in Tibet, China and found a collection different from any species previously known with axillary gemmae. It is characterized by the combination of slender plants, loosely attached leaves and solitary, dark red and flower-like gemmae, and it is here described as a new species.

Materials and methods
Microscopic examination was carried out using traditional methods. The collections of Pohlia and relevant species in the herbarium of 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 China Agricultural University (BAU) were examined.
Authors observed the plants under the dissecting microscope and examined the leaves and gemmae under the compound light microscope. Light micrographs were photographed using a Motic BA210digital microscope. All line drawings were made using the drawing tube attachments of these optical microscopes.  Table 1).
Etymology. The specific epithet tibetana refers to the type locality in Tibet in southwestern China.
Distribution and habitat. Currently Pohlia tibetana is only known from the type locality. This species grows on loose soil of rocks in the forest of Pinus armandii Franch.  (Shaw 1981a(Shaw , 1982(Shaw , 2006(Shaw , 2015Shevock and Shaw 2005;Guerra 2007;Uyar and Ören 2013;Wang et al. 2020). The detailed comparisons of plant and gemma morphological characters between them are shown in Table 1.
Among these species with singly axillary gemmae, P. inflexa and P. filum are most similar to P. tibetana in the features of plants (somewhat slender) and gemmae (subglobose). In P. inflexa, the gemmae are big (>500 μm long) and leaf primordia are conspicuous, pale to green, erect or somewhat incurved, while the gemmae are small (<300μm long) and leaf primordia are inconspicuous, the same color as the body and incurved in the new species. P. tibetana differs from P. filum by its yellowish brown or deep cherry-red, <300μm long (vs. orange or black and >300 μm long) gemmae and arising at apex as well as below, the same color as the body, incurved (vs. arising only in the apex, green to pale, erect) leaf primordia. The gemmae of P. tibetana are rather like those of P. andrewsii from Arctic regions (Shaw 1981b(Shaw , 2015Liu et al. 2018). Nevertheless, P. andrewsii is distinguished from the new species by its glossy leaves and densely clustered gemmae.
The propaguliferous species of Pohlia occurring in Tibet are very alike in habit and generally grow together, forming dense or lax turfs on soil. P. tibetana grows on loose soil mixed with two species of Pohlia having clustered axillary gemmae: P. flexuosa and P. hisae. The gametophyte features of P. tibetana, such as slender plants and spreading leaves which are somewhat contorted when dry, are very similar to P. flexuosa. The two species are confused with each other in the absence of gemmae. However, P. flexuosa is distinguished from P. tibetana by its dimorphic gemmae in dense clusters (Shaw and Torne 2009;Liu et al. 2018).
Suárez and Schiavone have conducted systematic research on the genus Pohlia in Latin America and published a series of achievements (Suárez and Schiavone 2010, 2011a, 2011b. In the revision of the propaguliferous Pohlia species (Suárez and Schiavone 2011a), the morphological characters of P. papillosa (Müll. Hal. ex A. Jaeger) Broth., such as loosely arranged leaves on the sterile plants in watery habitats, oblong or obconical gemmae in leaf axils orange or reddish with leaf primordia and body of the same color, are consistent with those of P. tibetana. In the former species, the gemmae are numerous in each axil and variable from linear-vermicular to obconical, leaf primordia erect, whereas in P. tibetana the gemmae are singly in each axil and stable rosebud shaped, and leaf primordia are inconspicuous with incurved apices.
The biodiversity of bryophytes in Tibet, China is very abundant. Eighteen species of Pohlia distributed in Tibet were recorded in Flora Bryophytorum Sinicorum (Li 2006