Schistidium relictum T.T. McIntosh, H.H. Blom, and E. A. Ignatova, 2017

Mcintosh, Terry T., Blom, Hans H., Kuznetsova, Oxana I. & Ignatova, Elena A., 2017, Schistidium relictum (Grimmiaceae, Bryophyta), a new moss species from Northwest North America and Siberia, Phytotaxa 299 (2), pp. 234-235 : 234-235

Schistidium relictum T.T. McIntosh, H.H. Blom, and E. A. Ignatova sp. nov., FIG. 1 .

Diagnosis: Schistidium relictum is a distinctive species, readily separated from other species of Schistidium by a number of gametophytic characters including dull, nearly black plants, with stems densely and evenly foliated, weakly spreading leaves that usually lack awns, the mostly 1-stratose distal leaf laminae with 2(–3) -stratose margins, a papillose distal abaxial surface of the costa, and a differentiated alar group of enlarged subquadrate cells delimited from adjacent cells. Also, its strongly differentiated perichaetial leaves are much larger than adjacent stem leaves, often hiding the sporophyte in lateral view. Also, its peristome teeth are long and curved.

TYPE:— CANADA. British Columbia: Mile 445, Alaska Highway, outcrop above creek, 59°05´N 125°49´E, 886 m, 26 August 1967, F. Boas 67071 (holotype UBC! B 106018, isotype TRH!).

Plants medium-sized to large, dull, nearly black or dark-brown, new growth yellow-brown, forming compact or loose mats, tufts, or cushions, sometimes partially buried in sand or silt. Stems (1.0–)1.5–2.5(–3.5) cm, dark, upper stems simple or branched (branching is less common in North American plants), usually somewhat curved, occasionally straight, arching-horizontal, ascending, or erect, densely and evenly foliate and somewhat ‘columnar-like’, with broad central strands. Stem leaves (1.2–) 1.4–1.8 (–2.0) mm long, 0.5–0.7(–1.1) mm wide, ovate-lanceolate, occasionally lanceolate or ovate-triangular, straight or slightly secund, sometimes in ± spiral rows, sharply keeled distally, broadly concave proximally, most leaves darker in the distal 1/2, when dry erect-appressed and sometimes with recurved apices, when wet patent to erecto-patent and recurved, 1-stratose, not decurrent; margins weakly recurved from base to about 2/3 (–4/5) of the leaf, smooth or papillose(-denticulate) distally, especially evident in young leaves, 2(–3) stratose distally in 1 or 2 rows; apices acute, rarely somewhat rounded; awns usually absent, when present short, to 0.1 mm, hyaline, terete, weakly denticulate or spinulose, usually not decurrent; costae strong, dark-coloured throughout, percurrent, dorsal surface often papillose distally, especially in young leaves, strongly bulging on abaxial surface for much of leaf length, in transverse section rounded near apex, broadened-elliptic, asymmetric and unevenly bulging medially and proximally, 2–3 cells thick; distal laminal cells (6–)8–9 μm wide, irregular in shape, short-rectangular or more or less isodiametric, occasionally oblate, walls moderately thick to thick, not sinuose, with small corner thickenings, smooth or with scattered, low papillae on the dorsal surface; medial laminal cells (8–)9–13 μm wide, short-rectangular, walls moderately thick, sinuose; basal cells 12–16 μm wide, rectangular or short-rectangular, thickwalled, weakly sinuose; alar cells differentiated as an area of enlarged and clear cells that are more or less isodiametric, short-rectangular, or, occasionally, rectangular especially along the margins, the alar region is 1–5 rows wide and 3–6 cells high (but smaller and less defined in North American material). Perichaetial leaves paler than stem leaves, (2.1–) 2.3–3.2 mm, broadly ovate or oblong with a triangular distal portion, erect, broadly acute, often with a short awn. Sexual condition gonioautoicous. Sporophytes common, immersed in perichaetial leaves or about 1/8 to 1/3 exposed. Seta (0.15–)0.3(–0.4) mm. Capsule urn reddish-brown to dark brown, short-cylindrical, (0.7–)0.8–1.0(–1.2) mm, sometimes slightly narrowed towards the mouth, shiny, occasionally striolate when dry; exothecial cells shortelongate or ± isodiametric, usually irregular in shape, sometimes 5 sided, sometimes oblate, rarely in lines, thin-walled or slightly and unevenly thickened, walls often curved; rim the same colour as capsule wall or darker and redder. Stomata (0–)2–6 at base of capsule. Peristome erect or patent, reflexed when dry, curved, not twisted along axis, 250– 450 μm, reddish-brown, usually densely papillose with very short papillae, usually perforated with slits, sometimes with small terminal prongs. Operculum usually short-conic, rostrate, rostrum straight or oblique. Spores yellowish, 9–12 (–14) μm, finely granulose.

Additional specimens examined: — CANADA. British Columbia: Summit Lake , 3 mi beyond N end, 58°35´N 124°40 E, Schofield 66179 ( UBC) ; Mt. St. George , 5300–5900 ft., 58°37´N 124°43´E, Vitt 11240 ( ALTA) ; Wokkpash Lake, SW shore, Mt. Roosevelt-Churchill Peak area , 58°45´N 124°85´E, Schofield, Vitt & Horton 66451 ( ALTA), 66619 ( ALTA, UBC) ; Muncho Lake area, Alaska Highway post 444.9 at Peterson Creek Bridge No 4, 58°52´N 125°49´E, Vitt & Andrus 3023 ( ALTA) ; Rocky Mts., Haworth Lake , 3800 ft., 58°47´N 125°07´E, Vitt 20096 ( ALTA, with Schistidium trichodon ) ; Yukon: Northern Ogilvie Mts., Nahoni Range , 65°37´N 139°06´E, Vitt 12963 ( ALTA, with Schistidium boreale ) ; Northern Ogilvie Mts., Nahoni Range , 4600–4700 ft., 65°37´N 139°03´E, Vitt 13073 ( ALTA) ; Northern Ogilvie Mts., Nahoni Range , 65°38´N 139°03´E, Vitt 13378 ( ALTA, NFLD) ; Northern Ogilvie Mts., Nahoni Range , 3900–4100 ft., 65°37´N 139°02´E ,, Vitt 13130, 13156 ( ALTA) ; mountain S of Mt. Klotz, at headwaters of Ogilvie River , 65°20´N 140°06´E, Vitt 7482 ( ALTA) ; Mackenzie Mts., Bonnet Plume Range, Wrightii Lake , ca 7.5. mi SE of Fairchild, 3300–4400 ft., 65°54´N 133°33´E, Horton 6701 ( ALTA), Vitt 16977 ( ALTA) ; Bonnet Plume Range, Riparium Lake , 4800–5200 ft., 64°46´N 133°23´E, Horton 6559 ( ALTA) ; South Richardson Mts., Doll Creek area , 66°05´N 135°48´E, Ritchie 7045 ( CANM) ; Peel River Watershed, Mt. Reception , site 36, 65°37´N 135°30´E, Bird & Benson 30496 ( CANM) ; N. W. T.: Inuvik, SE of Airport Lake along stream, Packer & Lemay 205 ( ALTA, with Grimmia teretinervis ) ; Mackenzie distr., Nahanni Range , just N of peak at 3598 ft., 61°43´N 123°20´E, Vitt 20290 ( ALTA, NY) ; Nahanni Range , 62°13´N 123°22´E, Horton 10403 ( ALTA) ; Mackenzie distr., Ram Range , 61°43´N 123°53´E, Vitt 20390 ( ALTA) ; Campbell Hills , 68°14´N 133°15´E, Scotter 28358 ( ALA, + Schistidium submuticum subsp. arcticum ) ; Gibson Ridge, Chick Lake , 1300 ft., 65°49´N 128°15´E, Gubbe & Burr 616 A ( ALTA) ; South Nahanni River Natl. Park, Deadman Valley , 61°19´N 124°35´E, Steere 76-325 ( NY) ; Kraus Hot Springs , 61°15´N 124°03´E, Steere 76-291 ( NY), Scotter 22530 ( NY) ; Virginia Falls , 61°38´N 125°42´E, Scotter 22349, 22259, 22260 ( NY) ; Nunavit: Devon Island , 75°40´N 84°40´E, Vitt 5354 ( ALTA) ; U.S.A. Alaska. Central Yukon River district, White Mts., limestone ridge, Gjaerevoll 18.VII.1953 ( TRH), Gjaerevoll 28.VII.1953 ( TRH) ; Chandalar Quad., Brooks Range, Sukapak Mt. , Spatt 631 ( ALTA) ; base of Sukapak Mt. , 610 m, 67°36´N 149°45´E Murray 77-121 ( ALA) ; Mountains NW of Walker Line, upper Kopuk River , above W end of Walker Lake , 67°10´N 154°30´E, Jordal 4041 ( MICH) ; Survey Pass Quad., vicinity of confluence of Alatna and Nahtuk rivers, 1200 ft., 67°25´N 153°43´E Murray 73-42 ( ALA) ; vicinity of Ambresvajun Lake (= Last Lake ), 1159 m, 68°38´N 143°41´E, Batten 75-43c ( ALA) ; Endicott Mts., Arrigetch Creek valley , 3400 ft., 67°26´N 154°05´E, Cooper CB-161, 4500 ft., 67°26´N 154°00´E, Cooper CB-165 ( ALA) ; Okpilak Lake vicinity, 69°25´N 144°03´E, Murray 8625 ( ALA) ; Toolik Lake, Wallace 18.VII.1976 ( ALA) ; Arctic Village, White mountain W of Chandalar River, 68°08´N 145°32´E, Steere & Iwatsuki 74-293 ( NY) ; RUSSIA ( ASIA): West Siberian Arctic, Yamalo-Nenetzky Autonomous District, Yunto Lake , 67°40´N, 68°00´E, 10.VIII.1993, Czernyadjeva 58 ( LE, MW) ; Krasnoyarsk Territory: Taimyrsky Autonomous District, State Biosphere Natural Reserve Taimyrsky , Medvezh’ya (Bear’s) River , slope of a limestone ridge along the right bank of Kotuy River , 70°58´N, 102°49´E, Fedosov 05-672 & 05-718 ( MW) ; Taimyrsky Autonomous District, right bank of Maimecha River 14 km downstream of Chopko Creek mouth, 70°50´N, 100°57´E, 30. VI.2009, Fedosov 09-46 ( MW) ; Republic Sakha / Yakutia: Bulun District , lower course of Lena River , Kharaulakh Mt. Ridge , Ogonnior- Yurege Creek , 170 m, 71°25´N, 127°25´E, 09.VII.2006, Pisarenko op04672 ( MW) ; Tompo District, Sette Daban Mt. Ridge, right bank of Segenyakh ( Rosomakha , or Wolverine ) Creek upstream Magadan Hwy , 470 m. 63°02´N, 137°57´E, 17.VII.2015, Ignatov & Ignatova 15-538 ( MHA, MW) .

Etymology: —The epithet relictum refers to a distribution pattern that suggests that S. relictum survived large parts of the Pleistocene glaciations in situ as a relict.

Distribution and Habitat:— Schistidium relictum is known from northwest North America and northern parts of Siberia in Asian Russia ( Fig. 2 ). Its elevation range is from ca 100–470 m in Siberia and ca 50–1700 m in North America. The species has a remarkable disjunct distribution pattern with most of the sites where it has been found having been unglaciated during long periods of the Pleistocene glaciations (e.g., Svendsen et al. 2004). We hypothesise that the species persisted in ice-free refugia north of the continental ice sheets during the Pleistocene, the huge Beringian refugium being the most important one (e.g., Hultén 1937, Schuster 1983). Its present distribution pattern probably indicates a low degree of migration in the Holocene following the retreat of the inland ice sheets.

Schistidium relictum is restricted to areas with occurrence of calcareous bedrock, especially limestones. It has been collected on dry ledges, walls, and boulders but also on periodically irrigated rocks on river banks, and occasionally on mineral soil. According to specimen labels and field data, there is a rather large variation in habitats from windswept ridges with little snow cover to adjacent to snow beds to moist sheltered sites in creeks and along rivers. Based on species admixtures in herbarium specimens, it grows with other Grimmiaceous calciphytes including Schistidium submuticum subsp. arcticum H.H.Blom , S. frisvollianum H.H.Blom , S. boreale Poelt , and Grimmia teretinervis Limpr.

The distribution of Schistidium relictum in North American resembles that of Andreaeobryum macrosporum Steere & B.M. Murray , which also occurs along the ice free corridor between the Laurentide and Cordilleran ice sheets in the Yukon-Northwest Territoiry-northern British Columbia area ( Pedersen et al. 2016). Further, Schistidium relictum was recently discovered in Yakutia, east Russia ( Ivanova et al. 2016), and, interestingly, was collected at this site along the same creek as Andreaeobryum macrosporum from 500 to 1100 m elevation. Both species are likely not rare in the mountains of this area.

Differentiation and relationships:— Schistidium relictum is a distinctive species only likely to be confused with other blackish Schistidium species, in particular S. andreaeopsis and S. boreale . Schistidium andreaeopsis is a much larger plant with longer leaves (2.0– 2.7 mm vs., on average, 1.4–1.8 mm) and wider distal leaf cells (10–12 μm vs. 8–9 μm). Also, its leaf cells are strongly sinuose to nodulose almost throughout and possess characteristic reddish walls, whereas they are esinuose or slightly sinuose in upper part of leaf and lack the reddish wall coloration in S. relictum . Sporophytes are unknown in S. andreaeopsis . The gametophyte of S. boreale is similar to S. relictum , but its leaf laminal cells are distinctly more densely and highly papillose and cells walls often reddish or orange. Also, the peristome teeth of S. boreale are shorter than those of S. relictum (220–330 μm vs. 250–450 μm).

Schistidium relictum appears to be rather isolated genetically based on molecular studies of total ITS ( Fig. 3 ). It is sister to the large clade, ‘Apocarpum’, which consists of species which probably embody its closest known extant relatives. Schistidium relictum shares the character states of long peristome teeth, papillose leaf costae, and denticulate upper leaf margins with several of these species. The tree in Figure 3 includes a basal paraphyletic clade formed by S. pulchrum , S. grandirete , S. sibiricum , and S. frisvollianum , and the main clade (PP=0.99) that includes all remaining species. The latter is subdivided into two clades, which, however, have low support. In contrast, high support is present for clades that correspond to the various sections, established by Blom (1996) based on morphological study, and clades from the previous broader analyses: Atrofuscum -clade (PP=1.00), Frigidum -clade (PP=0.96), Confertum -clade (PP=0.79, but P=0.99 for the main volume of this clade excluding S. tenerum ), Apocarpum -clade (PP=0.99), and, in addition, the clade formed by four specimens of S. relictum . The latter retains the sister position to the Apocarpum - clade, and, even though with only moderate support (PP=0.75), indicates the isolated position of S. relictum .

Figures

FIGURE 1. Schistidium relictum. A, F. Habit. B–C. Sporophytes, with and without operculum. D. Stem section. E. Cells of stem leaf apical portion with hyaline tip. G. Peristome tooth. H. Upper laminal cells. I. Median laminal cells. J. Basal laminal cells. K. Perichaetial leaf. L–N. Cauline leaves. O–R. Leaf transverse sections. S. Exothecial cells. Scale bars: 5 mm for F; 2 mm for A–C; 1 mm for K–N; 100 μm for D, G, O–R; 50 μm for E, H, I–J, S.

FIGURE 2. Global distribution of Schistidium relictum.

FIGURE 3. Illustration of genetic relationships of Schistidium relictum with selected species and species groups of Schistidium based on molecular studies of total ITS.