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Plagiothecium schofieldii, a new species from the Aleutian Islands (Alaska, USA)
expand article infoGrzegorz J. Wolski, Paulina Nowicka-Krawczyk, William R. Buck§
‡ University of Lodz, Łódź, Poland
§ Institute of Systematic Botany, The New York Botanical Garden, New York, United States of America
Open Access

Abstract

Plagiothecium schofieldii sp. nov. is described from the Aleutian Islands, Alaska, U.S.A. Some morphological features of this species correspond to P. lamprostachys (Southern Hemisphere species); however, Plagiothecium schofieldii is genetically and morphologically different from this and other common Northern Hemisphere species e.g., P. denticulatum, P. platyphyllum, or P. ruthei. The most important distinguishing morphological features differentiating this species are: the arrangement of the leaves on the stem; dimensions, concavity and symmetry of the leaves; dimensions of cells and their areolation; orientation of capsules. Additionally, due to the strong concavity of the leaves, they are very often badly damaged under the microscope. We present the results of DNA research of the analyzed samples, and a detailed description of the morphological features. The new species is illustrated, and its ecological preferences and currently known geographical distribution are presented. Additionally, the authors propose to add this species to Plagiothecium section, which is confirmed by morphological features and genetic analysis.

Keywords

Bryophyta, Plagiotheciaceae, taxonomy, W. B. Schofield

Introduction

Over the last several years, our perception has changed not only of Plagiothecium Schimp., but also of the whole family of Plagiotheciaceae M.Fleisch. (e.g., Pedersen and Hedenäs 2001, 2002; Wynns et al. 2018). The use of molecular methods has not only helped to understand many taxa previously considered problematic, but has also allowed for the description of a number of new taxa (e.g., Zuo et al. 2011; Wynns et al. 2018; Ignatova et al. 2019; Wolski and Nowicka-Krawczyk 2020). Nevertheless, for decades the taxonomic status of many species of this genus has been unclear and ambiguous, and those taxa currently require detailed morphological, genetic and taxonomic studies.

Although the Northern Hemisphere seems to be relatively well researched, there are still many areas (e.g., central Asia, Middle East) which remain as gaps on the world distribution map of Plagiothecium (Wolski et al. 2021). The results of taxonomic revisions conducted in recent years indicate the underestimation of the species richness of individual parts of the world. As a consequence of this research, many countries and regions have increased their number of ​known taxa of the described genus (e.g., Ellis et al. 2019a; Ellis et al. 2019b; Ellis et al. 2020, 2021; Müller and Wynns 2020; Wolski and Nowicka-Krawczyk 2020; Wolski 2020).

The Aleutian Islands, Alaska, U.S.A., are one of the many under-explored regions of the Northern Hemisphere. As a result of the taxonomic revision of Plagiothecium specimens from this area it was possible to describe a new species from this genus; the results are presented below.

Materials and methods

Taxonomic analyses

Material from the Missouri Botanical Garden (MO), The New York Botanical Garden (NY) and the University of British Columbia (UBC) was analyzed during the revision of Plagiothecium from the Aleutian Islands. For selected specimens intended for DNA analysis, appropriate consent was obtained from NY (NY02589541) and MO (MO5135779, MO5140205, MO5148015).

DNA isolation, amplification and sequencing

The molecular research was based on nuclear and chloroplast DNA markers: ITS (from the 3’ end of the hypervariable nuclear spacer ITS1, through the 5.8S gDNA, to the 5` end of the ITS2 spacer); and rpl16 cpDNA gene encoding ribosomal protein L16. Markers were selected based on Wynns et al. (2018), Ignatova et al. (2019) and Wolski and Nowicka-Krawczyk (2020) from Plagiothecium-focused studies.

Leafy stems of mosses were cut from dried material. Approximately 20 mg of dry tissue from each specimen in duplicates was placed in a 1.5 ml Eppendorf Safe-Lock tube and frozen (-20 °C) for homogenization. Tissue homogenization was performed using a hand-held stainless steel homogenizer (Schlüter Biologie, Eutin, Germany). Total DNA was extracted using the GeneMATRIX Plant & Fungi DNA Purification Kit (Eurx, Gdansk, Poland) following the manufacturer’s protocol. DNA extracts were quantified with a BioDrop DUO Spectrophotometer (BioDrop Ltd, Cambridge, U.K.). From the duplicates, the sample with the higher quality DNA (1.7–1.9 OD260/OD280) was selected for further analysis.

For each sample, all markers were amplified by PCR in a few replicates to obtain high quality amplicons for sequencing. PCR was performed using primers and reaction conditions as described in Wolski and Nowicka-Krawczyk (2020), with a 50 µl reaction volume with 25 µl of Color Taq PCR Master Mix (2×) (Eurx, Gdansk, Poland).

PCR products were visualized on an agarose gel (1.5%, 90V, 40 minutes) stained with GelRED fluorescent dye (Biotum, Fremont, CA, U.S.A.) and two replicates of each marker per sample were chosen for sequencing. Amplicons from the PCR reaction were cleaned using Syngen Gel/PCR Mini Kit (Syngen Biotech, Wrocław, Poland) according to the manufacturer’s protocol. Samples were sequenced with Sanger sequencing using primers from amplification by SEQme s.r.o. company (Dobris, Czech Republic). The obtained sequences were assembled in Geneious 11.1.5 (Biomatters Aps, Aarhus, Denmark) (http://www.geneious.com). The sequences were submitted to the NCBI GenBank database (www.ncbi.nlm.nih.gov) under the accession numbers MW936654- MW936657 for ITS and MW935831MW935834 for rpl16.

Phylogenetic analyses

Phylogenetic analyses of studied specimens and other species in the Plagiothecium group were performed based on a concatenated ITS-rpl16 sequence matrix. Voucher information for the specimens included in this study, with corresponding GenBank accession numbers, is presented in Table 1. Sequences were aligned using the MAFFT v. 7 web server (Katoh et al. 2017) (http://mafft.cbrc.jp/alignment/server/) where the auto strategy was applied, the scoring matrix of 200PAM with Gap opening penalty of 1.53, UniREf50 for Maft-homologs and Plot and alignment with threshold of 39 score were set. The obtained alignments were checked for poorly and ambiguously aligned regions and small corrections were made by eye. The evolutionary models were calculated using PartitionFinder 2 software (Lanfear et al. 2016) chosen according to the Akaike Information Criterion (Table 2).

Table 1.

Voucher information and accession numbers for the specimens included in the phylogenetic analyses.

Taxon Collection Locality ITS rpl16
Plagiothecium berggrenianum S-B44769 Russia: Pacific Siberia, Yakutiya KY550267 KY513972
Plagiothecium brasiliense E barcode E00387968 Brazil KY550266 KY513971
Plagiothecium conostegium NY: S.P. Churchill et al. 19839 Bolivia KY550271 KY513976
NY barcode 00845279 Guatemala KY550318 KY514024
S-B53327 Mexico KY550272 KY513977
Plagiothecium curvifolium DUKE barcode 0209096 Canada: BC KY550273 KY513978
CP: G.P. Rothero s.n. Germany: Hochschwarzwald KF882228 KF882328
Plagiothecium denticulatum CP: J.T. Wynns 2081 Denmark: Sorø kommune, Sjælland KF882229 KF882329
Plagiothecium denticulatum var. bullulae UC barcode 1947417 USA: CA KY550277 KY513982
UC barcode 1798690 USA: NV KY550278 KY513983
Plagiothecium denticulatumvar.obtusifolium CP: J.T. Wynns 2842 Germany: Schauinsland, Hochschwarzwald KF882230 KF882330
UC barcode 1724036 USA: WA KY550279 KY513984
Plagiothecium denticulatum fo. pungens DUKE barcode 0150010 USA: AK KY550280 KY513985
Plagiothecium laetum CP: J.T. Wynns 2907 Germany: Schauinsland, Hochschwarzwald KF882234 KF882334
C barcode CP0010626 USA: NC KY550292 KY513997
C barcode CP0010627 USA: NC KY550293 KY513998
OK2066 Germany MK934644 MK941642
OK2035 Russia: Krasnodar, Shakhe MK934647 MK941645
Plagiothecium lamprostachys S-B54613 Australia: VIC KY550284 KY513989
DUKE barcode 0156846 Australia: VIC KY550285 KY513990
Plagiothecium latebricola CP: I.L. Goldberg s.n. Denmark: Holmegårds Mose, Sjælland KF882235 KF882235
Plagiothecium lucidum NY barcode 01233548 Chile KY550298 KY514003
BONN: J.-P. Frahm 12–6 New Zealand KY550299 KY514004
Plagiothecium membranosulum BONN: J.-P. Frahm 7756 Democratic Republic of the Congo KY550310 KY514015
S barcode B78514 South Africa KY550303 KY514008
DUKE barcode 0016754 South Africa KY550304 KY514009
Plagiothecium mollicaule NY barcode 1596265 Brazil KY550300 KY514005
Plagiothecium ovalifolium DUKE barcode 0188886 Chile KY550314 KY514019
Plagiothecium pacificum UC barcode 1921143 USA: CA KY550295 KY514000
Plagiothecium platyphyllum CP: J. Lewinsky et al. s.n. Finland: Haluna, Nilsiae, Savonia borealis KF882241 KF882341
Plagiothecium rossicum OIK-2019 isolate OK2054 Russia: Kunashir MK934622 MK941625
OIK-2019 isolate OK2032 Russia: Smolensk MK934629 MK941630
Plagiothecium ruthei CP: J.T. Wynns 1997 Denmark: Lyngby Aamose, Sjælland KF882242 KF882342
Plagiothecium svalbardense C-M-9109 Greenland: W5 KY550296 KY514001
Plagiothecium angusticellum Wolski 22 Poland MN077507 MN311142
Plagiothecium longisetum Wolski 19 Poland MN077506 MN311141
Isopterygiopsis pulchella UC barcode 1947397 USA: CA KY550336 KY514042
P1 MO5135779 MO5135779 USA: Alaska, Simeonof Island MW936657 MW935834
P2 MO5140205 MO5140205 USA: Alaska, Simeonof Island MW936656 MW935833
P3 MO5148015 MO5148015 USA: Alaska, Simeonof Island MW936655 MW935832
P4 NY02589541 NY02589541 USA: Alaska, Adak Island MW936654 MW935831
Table 2.

Summary of partitions for ITS-rpl16 matrix (1574 bp) evolutionary model selection and phylogenetic interference using PartitionFinder2.

ITS1 5.8S gDNA ITS2 rpl16 intron rpl16 codon
ML JC JC HKY +I TIM+I+G JC
BI JC JC HKY F81 JC

Phylogenetic calculations were performed using maximum likelihood analysis (ML) in the IQ-TREE web server (Trifinopoulos et al. 2016) (http://iqtree.cibiv.univie.ac.at/) with the ultrafast bootstrap (UFBoot) pseudo likelihood algorithm (Hoang et al. 2018) and 10000 replicates; and Bayesian inference (BI) in MrBayes 3.2.2 (Ronquist et al. 2012) where two parallel Markov chain Monte Carlo (MCMC) runs for four million generations each, with trees sampled every 1000 generations. The average standard deviation of split frequencies in both cases remained below 0.01 for the last 1000 generations and posterior probabilities were estimated from the 50% majority-rule consensus tree after elimination of the first 25% of samples as burn-in. Raw data sequences, the alignment and tree files were submitted to the figshare online database (https://doi.org/10.6084/m9.figshare.14443697.v1).

Haplotype network analysis was performed using Median Joining Network in PopART v. 1.7 with gap coding as a single event irrespective of length and haplotypes` geographic distribution (Leigh and Bryant 2015). The analysis included species of Plagiothecium sect. Plagiothecium with representatives of P. longisetum and P. angusticellum (sect. Orthophyllum).

Results and discussion

Phylogenetic analyses based on the concatenated ITS-rpl16 matrix placed studied specimens within the branch of a Plagiothecium sect. Plagiothecium clade, or sister to it; however, the branch support was very low (BS = 49). The next branch down is to representatives of sect. Orthophyllum Jedl. and even more distant to sect. Leptophyllum Jedl. clade (Fig. 1). After branching off from the Orthophyllum clade, the internal division of sect. Plagiothecium was well supported by Bayesian inference (PP ≥ 0.98). Maximal support from both maximum likelihood and Bayesian Inference was recorded in the clade of Plagiothecium schofieldii, where the representatives create a monospecific clade (PP = 1).

Figure 1. 

Phylogenetic tree of Plagiothecium taxa with Isopterygiopsis pulchella as the outgroup based on concatenated nuclear (ITS1-5.8S-ITS2) and chloroplast (rpl16) DNA markers (total 1574 bp). The tree presents the position of Plagiothecium morphotypes from Alaska among the Plagiothecium group which is divided into individual sections. Numbers on branches indicate bootstrap values from ML followed by posterior probabilities from BI analysis. Asterisk (*) indicates 100 (ML) and 1.00 (BI), while minus (-) indicates values below 50 (ML) and 0.7 (BI). The topology of the tree was based on ML analysis.

The haplotype network (Fig. 2) also showed internal diversity in sect.Plagiothecium. At the center, the analysis grouped haplotypes from the Northern Hemisphere (P. denticulatum and P. ruthei). Three branches extending from the center apply to haplotypes from Central America and the Southern Hemisphere. The position of P. schofieldii haplogroup is fairly isolated and consists of two haplotypes: the first refers to three specimens from Simeonof Island, while the second to a representative from Adak Island (Table 1); however, as it grows in the Aleutian Islands, Alaska, the branch vector points out the same direction as haplotypes from the Northern Hemisphere.

Figure 2. 

Median-joining haplotype network of sections Plagiothecium and Orthophyllum of Plagiothecium constructed in PopART. Haplotypes are represented by circles with colors indicating geographic distribution. The number on the branches indicates the mutational steps.

The individual taxonomic features of Plagiothecium are related to a specific level of detail in our analyses, and for example: superficial layer of the stem (epidermis layer) of large, thin-walled cells; shortly pointed leaves; serration (if present) only at apex; absence of pseudoparaphyllia; leaves clearly decurrent at the base – distinguish this genus from other genera belonging to the Plagiotheciaceae. Within Plagiothecium, the shape of decurrent alar regions, and the shape of their cells distinguishes the species of individual sections, while the shape and dimensions of leaf cells are the most important features distinguishing species from each other (Iwatsuki 1970; Lewinsky 1974; Noguchi 1994; Smith 2001). Therefore, based on the fact that the analyzed specimens have decurrent alar cells that are rounded, inflated, and form distinct auricles, as well as the shape and size of the leaf cells of Plagiothecium schofieldii, we believe that this species belongs to Plagiotheciumsect. Plagiothecium. This is also confirmed by molecular and haplotype network analyses.

Species that are widespread in the Northern Hemisphere: Plagiothecium denticulatum (Hedw.) Schimp., P. platyphyllum Mönk., and P. ruthei Limpr., significantly differ in morphology from P. schofieldii, which, compared to the above-mentioned species, has erect stems, while the others are usually prostrate, or sometimes prostrate to ascending (Smith 2001; Li and Ireland 2008; Wynns 2015).

Leaves of P. schofieldii are julaceous and imbricate – very closely arranged on the stem, while in other species the leaves are strongly complanate, flaccid, and spreading on the stem. In the Northern Hemisphere only in P. denticulatum shoots are rarely julaceous (Lewinsky 1974; Smith 2001; Li and Ireland 2008; Wynns 2015). The appearance of the mats and the arrangement of the leaves on the stem are more similar to those features in P. cavifolium (Brid.) Z. Iwats. (which belongs to Plagiothecium sect. Orthophyllum).

Stem leaves of Plagiothecium schofieldii are very strongly concave, to such an extent that under the microscope they are clearly damaged and cracked from being flattened by the coverslip. The leaves of the closely related species are rather flat. Only in the case of P. denticulatum are the leaves more or less concave, but never to such an extreme (Lewinsky 1974; Smith 2001; Li and Ireland 2008). Plagiothecium schofieldii is characterized by symmetrical leaves, and from other members of sect. Plagiothecium only P. platyphyllum has more or less symmetrical leaves, but this is the only feature common to both species. Symmetrical leaves are typical, e.g., for species from sect. Orthophyllum (e.g., P. nemorale, P. cavifolium) (Lewinsky 1974; Smith 2001; Li and Ireland 2008; Wynns 2015; Wolski 2020). Also, leaves of P. schofieldii are clearly longer and wider than those of all the species mentioned above (Smith 2001; Li and Ireland 2008).

Plagiothecium schofieldii is clearly distinguished from P. denticulatum, P. platyphyllum and P. ruthei by the length and width of it laminal cells. The cells located in the central part of the leaf are long and very wide (88–190 × 13–29 μm), which makes the cell areolation very loose. None of the above-mentioned species has such long and broad cells, and thus their cell areolation is tighter (Lewinsky 1974; Smith 2001; Li and Ireland 2008).

Another feature that clearly distinguishes this newly described species from the previous species in sect. Plagiothecium is the orientation of the capsules. In the studied specimens of P. schofieldii, the capsules are orientated most often more or less vertically, i.e., erect, rarely inclined. Plagiothecium denticulatum, P. platyphyllum, and P. ruthei have inclined capsules (Lewinsky 1974; Smith 2001; Li and Ireland 2008; Wynns 2015).

On the other hand, in terms of morphology, P. schofieldii looks more like P. lamprostachys (Hampe) A. Jaeger – a Southern Hemisphere species (Ireland 1992; Wynns 2015) – than the common Northern Hemisphere species mentioned above. Both the morphological features and molecular analyses indicate the distinctiveness of the species (Figs 14).

Additionally, Wynns (2015) pointed out that P. lamprostachys forms a clade within P. denticulatum sensu lato, which is also confirmed by our research (Fig. 1). Phylogenetic analyses of concatenated nuclear and chloroplast markers placed P. schofieldii within sect. Plagiothecium next to P. denticulatum; however, the branch support was very low. After branching off from the Leptophyllum clade (BI = 0.70), Bayesian inference highly supported the phylogenetic relations within sect. Plagiothecium indicating the separateness of a P. schofieldii clade (as well as a sect. Orthophyllum clade). This separation was also visible in the haplotype network, where the analysis extended the Alaskan clade far from the center of the network grouping species of Plagiothecium from the Northern Hemisphere.

All the above morphological data, supported by molecular studies, warrant the recognition of the Aleutian samples as a new species.

Taxonomy

Plagiothecium schofieldii G.J.Wolski & W.R.Buck, sp. nov.

Type

U.S.A. Alaska, Shumagin Islands, Simeonof Island, mainly near saddle between Hill 1436 and 1265, wet cliff chimney, 54°55'N, 159°15'W, 19 July 1996, W.B. Schofield 106119, Holotype MO5135779.

Description

Plants small, light green to yellow, with a delicate metallic luster, forming very dense, often homogeneous mats. Stems erect, 1.5–3.0 cm long (Fig. 3), in cross-section rounded, with a diameter of 300–380 μm, the central strand developed, epidermal cells 10–25 × 6–12 μm, the parenchyma thin-walled, 20–40 × 15–32 μm; leaves julaceous, imbricate, very closely arranged on the stem, when dry not shrunken, very concave, therefore very often damaged under the microscope, symmetrical, ovate to elliptic, those from the middle of the stem 1.4–3.0 mm long, and the width measured at the widest point 0.9–1.9 mm; the apex obtuse and apiculate, often denticulate; costae two, thick and strong, extending usually to ½ of the leaf length, reaching 0.5–2.0 mm; laminal cells linear, rather symmetrical, in quite regular transverse rows, the length and width very variable but dependent on location: 66–178 × 14–33 μm at apex, 88–190 × 13–29 μm at midleaf, and 45–221 × 20–39 μm toward insertion, due to the very wide cells, cell areolation clearly loose; decurrencies of 4–5 rows of rounded, rounded-rectangular, inflated cells, 40–90 × 22–48 μm, forming distinct, quite long auricles, 300–750 μm long (Fig. 4). Autoicous. Sporophytes abundant; setae dark brown at base, yellowish-orange at apex, twisted when dry, 1.8–2.3 cm long; the capsules more or less erect, 700–950 × 280–350 μm; operculum short and rostellate; peristome double, well developed, 450–500 μm long; exostome teeth trabeculate at the ventral side.

Figure 3. 

Stems with the sporophytes of Plagiothecium schofieldii. Part of the turf of holotype (W.B. Schofield 106119, MO5135779). Scale bar: 1 cm.

Figure 4. 

The most important taxonomic features of Plagiothecium schofieldii. Dimensions of cells from the apex A the middle B and basal part of the leaf C leaves D–E leaf apex F auricles G. Scale bar: 100 µm (A–C, F–G); 500 µm (D–E). Photos from the holotype (W.B. Schofield 106119, MO5135779).

Etymology

The present species is named in honor of Wilfred “Wilf” Borden Schofield (1927–2008), who spent decades studying northern regions of North America, including the Aleutian Islands, and who on July 19, 1996, collected the specimen (No. 106119), chosen here as the holotype of Plagiothecium schofieldii. According to Stephen Talbot (pers. comm.), Schofield recognized this plant as distinct in the field.

Distribution and ecology

Plagiothecium schofieldii so far has only been recorded from Adak Island, Attu Island and Simeonof Island in Alaska. In this area it has been recorded on wetlands and hills, wet cliff chimney, open, moist crevice of a cliff, shaded face of hole on slope, shaded humid outcrop, along creek and adjacent slope, near saddle between hills and near base of mountain.

Additional specimens examined

U.S.A. Alaska: Adak Island, Finger Bay, along creek and adjacent slope, open, moist, crevice of cliff, 15–30 Jun 1975, D. K. Smith 3864 (NY02589541); Attu Island, near Jaemin Pass, slopes of Ribson Ridge, shaded face of hole on slope, 52°53'N, 173°10' W, 10 Aug 2000, W. B. Schofield & S. S. Talbot 115646, UBC ACC# B185126; Shumagin Islands, Simeonof Islands, near base of larger mountain, N. side, 54°55'N, 159°15' W, shaded humid outcrop, 17 Jul 1995, W. B. Schofield, S. S. Talbot & G. Argus 104056, ACC# B159650 (MO5140205); wetlands and Hill 624, 54°55'N, 159°15'W, seepy cliff chimney, 7 Jul 1996, W. B. Schofield 105769, ACC# B161483 (MO5148015).

Acknowledgments

We thank the late Dr. Judy Harpel for the opportunity to revise the Aleutian Plagiothecium species. The research was funded from a grant Genetic study on variability of selected taxa of the genus Plagiothecium NCN „Miniatura 4” – DEC-2020/04/X/NZ8/00420.

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