The complete plastome of Polytrichum commune Hedw. (Polytrichaceae, Bryophyta)

Abstract Polytrichum commune, one of hair-cap mosses, is the type species of the genus Polytrichum Hedw. (Polytrichaceae). Here we present its complete plastome. The plastome of P. commune is successfully assembled from raw reads sequenced by HiSeq X ten system. Its total length is 126,323 bp consisting of four regions: large single copy (LSC) region (88,070 bp), small single copy (SSC) region (16,717 bp), and inverted repeats (IRs; 9,680 bp per each). It contains 128 genes (84 coding genes, eight rRNAs, and 36 tRNAs); nine genes (four rRNAs and five tRNAs) are duplicated in IR regions. The overall GC content is 28.9% and in the LSC, SSC and IR regions is 26.1%, 25.1%, and 45.5%, respectively. This plastome is an important sequence resource for further studies on the class Polytrichopsida.

Polytrichum commune Hedw., commonly known as a hair-cap moss, has been used as a traditional Chinese medicine as it has anticancer activity (Fu et al. 2009;Yuan et al. 2015). It shows clear differentiation of water-conducting tissue (hadrom and leptom), which is analogous to vascular tissue (xylem and phloem) of higher plants (Eschrich and Steiner 1968). Polytrichum is distinguished from the allied genus Pogonatum P. Beauv. by capsules with stomae (Smith and Gary 2007). Recent molecular phylogenetic studies presented that P. commune is a crown group of the family Polytrichaceae (Hyv€ onen et al. 2004), which is the sole member of the class Polytrichopsida. Till now, Pogonatum inflexum (Lindb.) Sande Lac. is the only available complete chloroplast genome of Polytrichopsida in GenBank. Polytrichum juniperinum Hedw. and Polytrichum strictum Menzies ex Brid. have only partial chloroplast genome data (de Freitas et al. 2018). Here, we present the plastome of P. commune as a first complete plastome of Polytrichum, the type genus of Polytrichaceae.
Phylogenetic trees show that class Polytrichopsida (P. commune and P. inflexum) is sister to class Tetraphidopsida (Tetraphis pellucida Hedw.), which is in accordance with previous studies (Volkmar and Knoop 2010;Liu et al. 2019) (Figure  1). In addition, a basal clade was formed by Sphagnum palustre L. (Shaw et al. 2016) and Takakia lepidozioides S. Hatt. and Inoue (AP014702), which is same as the result of Cox et al. (2004) and Qiu et al. (2006), but is incongruent with Liu et al. (2019). In summary, this suggests that additional bryophyte chloroplast genomes are needed to elucidate the phylogenetic relationships of these species. With the help of next generation sequencing technology, more and more plastome sequences of mosses will be published in the near future, which will allow us to have a better understanding of their phylogenetic relationships.

Disclosure statement
The authors are really grateful to the open raw genome data from public database. The authors report no conflicts of interest and are responsible for the content and writing of the paper.

Funding
This research was supported by the Fundamental Research Funds for the Central Universities.

Data availability statement
The genome sequence data of Polytrichum commune that support the findings of this study are openly available in GenBank of NCBI at (https:// www.ncbi.nlm.nih.gov/) under the accession no. MW528408. The associated BioProject, Sequence Read Archive (SRA), and Biosample numbers are PRJNA698729, SRR13608611, and SAMN17734892, respectively.