Taxonomic and nomenclatural novelties in Syntrichia ( Bryophyta : Pottiaceae ), with reinstatement of an endemic continental Antarctic species

. Taxonomic implications of the phylogeographic studies based on multilocus sequencing of nuclear and chloroplast DNA regions of Syntrichia sarconeurum , long considered to be Antarctic endemic moss species, are summarised. Molecular analyses confirmed the conspecificity of Syntrichia sarconeurum with S. lithophila and S. pygmaea . This taxonomic conclusion implies that the correct name for the species in the genus Syntrichia is S. lithophila and S. sarconeurum is a new synonym of this name. It is because S. sarconeurum takes priority from 2007, whereas S. lithophila is based on Tortula lithophila which was validly published in 1906 and it is the next earliest legitimate name at the rank of species to be used. Syntrichia sarconeurum , as traditionally conceived, proved to be a heterogeneous taxon actually consisting of two distinct species, namely S. lithophila and S. frigorideserticola nom. nov., which is a new name for Sarconeurum antarcticum whose epithet is not available in Syntri-chia . Australian and New Zealand plants of Syntrichia with propaguloid leaf apices are definitely distinct from South American and Antarctic S. lithophila and S. frigorideser-ticola and the correct name for them is S. abruptinervis comb. nov., based on Tortula abruptinervis .


Introduction
The moss genus Syntrichia Brid., as traditionally circumscribed, is one of the largest genera of the Pottiaceae and consists of about 80 species that are distributed on all continents (Crosby et al. 2000).In the Antarctic it is represented by five species and one variety that are mainly distributed in the Antarctic Peninsula region of West Antarctica.Only two species, S. magellanica (Mont.)R. H. Zander and S. sarconeurum Ochyra & R. H. Zander, are generally considered to be panantarctic in distribution, the latter of which appears to be widespread and locally common in continental East Antarctica (Ochyra et al. 2008).
Syntrichia sarconeurum is a very distinctive species of moss in the Antarctic, which differs from all other species in this biome by having fleshy and swollen, deciduous leaf apices forming caducous propagules which are often present on some leaves in the apical comal group.The only other species in Antarctica which possess such propaguloid leaf apices are two species of Tortella (Lindb.)Limpr., T. fragilis (Drumm.)Limpr.and T. alpicola Dixon, which are immediately distinguished from S. sarconerum by their hyaline basal cells that are highly differentiated from the upper chlorophyllose cells and extend strongly up the margins to form a distinct V-shaped basal region.In contrast to Tortella species, the hyaline basal cells in S. sarconeurum are differentiated juxtacostally across the leaf base, and the junction line with the upper chlorophyllose cells is gradual and not sharply defined.In addition, S. sarconeurum only has an adaxial stereid band in the costa, whereas Tortella species have adaxial as well as abaxial stereid bands.
As indicated on the label of one of the syntypes in the Mitten herbarium at NY, Syntrichia sarconeurum was first collected by J. D. Hooker on 6 January 1843 on the small Cockburn Island off the north-eastern coast of the Antarctic Peninsula during the British Antarctic Expedition 1839−1843, under the command of Captain James C. Ross (Headland 1989).It was described and illustrated by Wilson & Hooker (1847)  species and placed it in the genus Didymodon Hedw.with a question mark.It was an unfortunate choice of the specific epithet because these authors overlooked the name D. glacialis (Funck ex Brid.)Wallr.(Wallroth 1831: p. 184), which made the name of their new species an illegitimate later homonym.However, the epithet glacialis was soon legitimised as Leptotrichum glaciale Müll.Hal.(Müller 1851: p. 611).
In 1899 Carsten E. Borchgrevink, a leader of the British-financed Southern Cross Expedition of 1898−1900, which was the first British venture of the Heroic Age of Antarctic exploration, collected a moss in Victoria Land in continental East Antarctica which was reported by Gepp (1902) as an unnamed species of Barbula Hedw.It was soon described by Bryhn (1902) as a new genus and species, Sarconeurum antarcticum Bryhn.Subsequently, the species was rediscovered on Ross Island off Victoria Land by the British Discovery Expedition of 1902−1903 under the command of Robert F. Scott (Headland 1989).The material was examined by Cardot (1907) who found that it was identical to Leptotrichum glaciale of Müller (1851) and to Sarconeurum antarcticum.Considering the unique habit of this species due to the propaguloid leaf apices, Cardot (1907)  Caducous leaf apices are not unique to Sarconeurum glaciale but they are also known in other species of pottialean mosses, including the Fuegian Tortula lithophila Dusén and T. pygmaea Dusén which are now considered conspecific, the former name having priority (Ochyra & Zander 2007).The ostensible morphological similarity of these three species prompted Greene (1975) to consider them identical, thereby extending the geographical range of S. glaciale to Patagonia and Tierra del Fuego in southern South America.Ochyra & Zander (2007) accepted the congenericity of Sarconeurum and Syntrichia because they found that the generitype of the former, Sarconeurum antarcticum which was then considered to be conspecific with S. glaciale, fits perfectly into the concept of Syntrichia sect.Aesiotortula R. H. Zander.As a result, this species was transferred to the genus Syntrichia, but its name was changed to Syntrichia sarconeurum which was published as an explicit substitute for the legitimate name Leptotrichum glaciale because the epithet glacialis was unavailable in Syntrichia due to S. glacialis (Kunze ex Müll.Hal.) R. H. Zander (Zander 1993: p. 269).At the same time these authors accepted S. lithophila to be a distinct species, though closely related to S. sarconeurum (Ochyra & Zander 2007).
A taxonomic treatment of the Antarctic species of Syntrichia with caducous leaf apices, including an identification key, descriptions and geographical distribution, will be published separately.The present account intends to address the taxonomic and nomenclatural implications of the phylogeographic studies of the broadly conceived S. sarconeurum based on molecular analyses (Saługa et al. 2022).

Materials and methods
The work is based on a comprehensive study of the relevant literature concerning the Antarctic representatives of the genus Syntrichia and related South American and Australasian taxa to propose adequate taxonomic and nomenclatural changes congruent with a recent detailed genetic assessment of the samples from the whole geographical range of the species concerned (Saługa et al. 2022).The analysis of morphological features relied upon examination of extensive herbarium collections from KRAM and nomenclatural changes are based upon study of the type specimens from BM, FH, L, NY, O, PC, S and UPS.The proposed nomenclatural changes have been implemented in accordance with the relevant provisions of the International Code of Nomenclature for algae, fungi, and plants (ICNafp) (Turland et al. 2018).

Results and discussion
As presently circumscribed, Syntrichia sarconeurum is morphologically a very variable species (Ochyra et al. 2008) and its phenotypic plasticity is coupled with the conspicuous genetic variation (Selkirk et al. 1997;Skotnicki et al. 1999Skotnicki et al. , 2000Skotnicki et al. , 2004)).With the recent availability of new molecular data, it has been firmly established that the different representatives previously referred to this taxon, should no longer be considered as representing one and the same species (Saługa et al. 2022).Phylogenetic reconstruction, in particular that based on ribosomal nuclear sequences, as well as network estimation of all known haplotypes from southern South America (Patagonia), East and West Antarctica, identified three main genetic lineages demarcating the clear separation between specimens from Patagonia, the peri-Antarctic archipelagoes of the South Orkney Islands and the South Shetland Islands, the Antarctic Peninsula region south to Alexander Island, as well as Coats Land and Dronning Maud Land (continental Antarctica) on the one hand and those from the remaining coastal and inland areas of the Antarctic continent on the other.A genetic discontinuity has also been found within specimens from Victoria Land localities corresponding, geographically, to the position of the Borchgrevink Coast versus Dufek and Scott Coast.These genetic results strongly challenged the taxonomic status of S. sarconeurum and show that an extended biosystematic analysis is needed to draw reliable conclusions at the taxonomic level.Published multilocus analyses have converged with conclusions based on morphological studies, providing additional support for this view.However, the morphological diversification between specimens from different parts of Victoria Land has not been confirmed.
As a result of detailed molecular and morphological studies, Syntrichia sarconeurum is considered conspecific with S. lithophila as some earlier authors suggested (Greene 1975;Matteri 1982Matteri , 1985;;Lightowlers 1985).However, according to Art. 11.4 of the ICNafp (Turland et al. 2018) the correct name for the ultimate species has to be S. lithophila which is based on Tortula lithophila, a legitimate name validly published in 1906 (Dusén 1906) and it is the next earliest legitimate name at the rank of species to be used.In contrast, S. sarconeurum takes priority from 2007 when it was published as an explicit substitute for the legitimate names Leptotrichum glaciale and Sarconeurum antarcticum because the epithets glacialis and antarctica were unavailable in Syntrichia since they were blocked by Syntrichia glacialis (Müll.Hal.) R. H. Zander and S. antarctica (Hampe) R. H. Zander (Ochyra & Zander 2007).
Syntrichia lithophila occurs in Patagonia and Tierra del Fuego in southern South America, in the Antarctic Peninsula region in West Antarctica and on Coats Land and Dronning Maud Land in westernmost East Antarctica.On the other hand, the plants widely distributed in East Antarctica, from MacRobertson Land to Victoria Land and Marie Byrd Land, were originally described as Sarconeurum antarcticum which is here reinstated as a species in its own right.This species is named Syntrichia frigorideserticola Ochyra, Saługa & Ronikier which is published as an explicit substitute for Sarconeurum antarcticum under Art.6.11 of the ICNafp (Turland et al. 2018) because the epithet antarcticum is blocked in Syntrichia by S. antarctica (Hampe) R. H. Zander (Zander 1993: p. 267).
Finally, the Australian and New Zealand plants once determined as Syntrichia pygmaea (Zander 1993;Streimann 1997;Streimann & Klanzenga 2002) are definitely distinct from South American and Antarctic ones, as also supported by the genetic data (Saługa et al. 2022).Actually, they represent a separate species which was originally described from New Zealand as Tortula abruptinervis Dixon (Dixon 1923), which was subsequently considered identical to S. pygmaea by Zander (1993: p. 267) who also intended to transfer this species to Syntrichia but the relevant new combination was not validly published because the basionym was not cited.It is validated here.
Notes.(1) When describing Tortula lithophila, Dusén (1906) used initially the epithet lithopila.It was an orthographic error which was immediately corrected by the author elsewhere in the same paper and the epithet lithophila is generally accepted for this species.It is worth noting that Dusén (1905) originally described this species as Tortula saxicola but he soon discovered that this name was a later homonym of T. saxicola Cardot, a species described one month and a half earlier, on 31 October 1905, by Cardot (1905), also from material collected in Tierra del Fuego.Accordingly, a year later Dusén (1906) substituted the illegitimate name T. saxicola Dusén for T. lithophila.