Orthothecium strictum Lorentz, Moosstudien

6. Orthothecium strictum Lorentz, Moosstudien View in CoL , 122. 5d. 1864.

— O. rubellum (Mitt.) Kindb., Bih. Kongl. Svenska Vetensk.-Akad. Handl. 7(9): 46. 1883. — Stereodon rubellus Mitt., J. Proc. Linn. Soc., Bot. 8: 40. 1864. — O. binervulum Molendo in Lorentz, Moosstudien, 120. 1864. — Figs. 14–16 View Fig View Fig View Fig , 17B–V View Fig , 18–21 View Fig View Fig View Fig View Fig , 22C–D View Fig .

Plants small, rarely medium-sized, golden-, brownish- or reddish-green, glossy. Stems procumbent or ascending, to 2.5 cm long, terete-foliate, irregularly branched. Leaves erect-spreading or appressed (exceptionally homomallous, see discussion of OK2481 below), 0.8– 1.7(–2.2)× 0.2–0.6 mm, ovate-lanceolate or lanceolate, acuminate, slightly narrowed to insertion, not decurrent, moderately concave, non-plicate or slightly plicate in some leaves, especially in younger parts of plants; margins narrowly recurved for most of leaf length on both sides, rarely only in one side; cells in mid-leaf (40–)50– 85×5–9 µm, with moderately thickened, weakly porose walls; basal leaf cells in 1–2 rows shorter and wider, porose, alar cells not differentiated. Specialized asexual reproduction by axillary gemmae rarely present, gemmae 60–85×12–18 µm. Sporophytes very rare (described here for first time based on specimen OK2481, with anomalous gametophyte morphology, Fig. 21 View Fig ). Setae ca. 1 cm. Capsules short cylindrical, 0.9–1.1 mm long, slightly inclined, slightly curved. Exostome teeth ca. 300 µm long, whitish or yellowish-white, striolate below, papillose above; endostome with basal membrane ca. 150 µm high, segments narrow, perforate, cilia 2, nodose. Spores 12–15 µm.

Distribution and ecology. Orthothecium strictum is a circum-Holarctic arctic-alpine species. It penetrates southward in Eurasia to Central Europe, Mongolia and Tibet, in North America to Colorado. In European Russia it occurs in northern regions where rocky substrates are abundant, and in the North Urals; in Asian Russia it is widespread in the mountains and in Arctic regions; in the south of the Russian Far East it was found only in Sakhalin Island. It occurs in a wide altitudinal range, from the sea level (in Kamchatka) to 2800 m (in Altai Mts), and 5400–5800 m in Tibet, growing on wet, shady limestone and gypsum cliffs and rock outcrops, arctic and mountain tundra, in niches between rocks of rockfields.

Additional selected specimens examined: EUROPEAN RUSSIA: Arkhangelsk Province: Franz Josef Land: Hooker Island, Sedov Cape, 1929, I.M. Ivanov s.n. (LE); Alexandra Land Island, south of Nagurskaya station, 29.VII.2012, Kholod 11 (LE); Fersman Island, 7.VIII.2012, Kholod s.n. (LE); Georg V Land Island, Kholod s.n. (LE); ASIAN RUSSIA: Yamalo-Nenetsky Autonomous District: Yunto Lake, 12.VIII.1994, Czernyadjeva 93 (LE); same place, 10.VIII.1993, Czernyadjeva 58 (LE). Krasnoyarsk Territory: Vise Island, 14.VIII.1932 V.P. Savicz 1562 (MHA, LE); Jenisei, Mjelnitsa, 13.VII.2876, Arnell s.n. (S, B213763); Taimyrsky Autonomous District, Kayak Settl., Kotui River, Fedosov 07-830 (MW 9075084); western Taimyr, right bank of Pyasina River near Tareya Settl., 15.VII.1966, Matveeva s.n. (MW 9075083). Yakutia: Lensk District, Pilka River basin, 25.VII.1999, E.I. Ivanova s.n. (MHA ex SASY); Olenyokskiy Distr., Daldyn River basin, 29.VI.1956, Lukicheva & Zagrebina s.n. (LE); Tomponsky Distr., Sette-Daban Mt. Range, Segenyakh (Rosomakha) Creek, Ignatov & Ignatova 15-586 (MHA 9029737); Eveno-Bytantaysky Distr., Orulgan Mt. Range, Enigan-Toolono Creek, 8.VIII.2011, Isakova 439 (MHA ex SASY); Khangalassky Distr., Lenskie Stolby near Labydja Creek mouth, Ignatov 00-223 (MHA); Oymyakon Distr., Suntar-Khayata Mt. Range, Mus-Khaya Mt., Ignatov & Ivanov 11-3535 (MHA). Altai Republic: Ak-Turu, 19.VII.1966, Bardunov s.n. (MHA); Kuraiskij Mt. Range north of Kosh-Agach, 1.VIII.1992, Ignatov 31/183 (MHA).

EUROPE: Norway: Nord-Trøndelag Province, Røyrvik Distr., 18.VII.2014, Hedenäs s.n. (S, B205284); Svalbard, Advent Bay, 1926, Lagerkranz s.n. (S, B213723). Sweden: Jämtland Province, 19.VII.1882, Adlerz s.n. (S, B213525); Torne lappmark Province, Jukkasjärvi, VII.1944, Hülphers s.n. (S, B213631); Lule lappmark Province, Kvickjock, Kaddepakti, 29.VII.1867, Holmgren s.n. (S, B213549); Lycksele lappmark Province, Tärna, Hülphers s.n. (S, B213540). Finland: Koillismaa Province, Kuusamo Distr., VIII.1883, Brotherus s.n. (S, B213709). Italy: Veneto Province, Belluno Distr., 25.VIII.1907, Pampanini 889 (S, B213762). Switzerland: Graubünden, Rhaetia Val Duana, 20.VII.1868, Pfeffer s.n. (S, B213769).

NORTH AMERICA: Canada: Northwest Territories, Ellesmere Island, 0. VIII.1967, Brassard 3236 (S, B213888); Yukon Territory, 8.VII.1973, Vitt 7978 (S, B213887). Greenland: Narssaq, 26.VIII.1962, Steere 62-1153 (S, B213886). U.S.A.: Alaska, Umiat and vicinity, Colville River, 21-26.VII.1951, Steere 17145 (S, B213954).

Differentiation and variation. Orthothecium strictum is distinguished by a combination of the following characters: small size of plants; terete foliate stems; erect to erect-spreading leaves, occasionally appressed or widely spreading, lanceolate or ovate-lanceolate, not or weakly plicate [when dry], narrowly acute or acuminate; leaf margins entire or weakly serrulate near apex, and narrowly recurved for most of leaf length or partly so. Its differences from O. brunnescens and O. remotifolium are discussed under those species. Orthothecium intricatum is similar to O. strictum (especially to its narrow-leaved morphs) in its plant and leaf size but has usually slightly homomallous leaves and flat leaf margins. Homomallous leaves are rare in O. strictum except for specimens collected at one locality in Yakutia, Ulakhan-Chistay Mt. Range, which have falcate-secund leaves with narrowly recurved margins (isolate OK 2481; Fig. 21 View Fig ). This is the only known collection of this species with sporophytes.

Both ITS and chloroplast data agree on the support for the lineage, annotated as O. strictum 1 in the phylogenetic trees. The plants with this multilocus genotype are morphologically rather homogeneous, corresponding perfectly to the description of O. strictum ( Lorentz, 1864) as small, high-alpine cryophilous plants, occurring in corresponding biotopes throughout the Northern Hemisphere. Most of the molecularly barcoded specimens of O. strictum 1 lineage are from the region extending from Alaska through Magadan Province and Yakutia to Mongolian and Altaian highlands, and also in Anabar Plateau in the southern Taimyr. However, two specimens of the same genotype were discovered in high-alpine regions of Austria, with one them even from the same mountain range where the type locality of O. strictum occurs (Köckinger 15250, isolate Ot1959: Austria: Tyrol, Hohe Tauern, Mt Säulkopf, Fig. 17B View Fig ). The plants match morphologically the isotype of O. strictum ( Fig. 18 View Fig ). However, we are at present not able to distinguish such plants morphologically from small plants belonging to the other three lineages within O. strictum s.l., although these lineages often contain markedly more robust plants, with leaves often at least slightly plicate and having sometimes markedly remote-leaved foliage.

It is not impossible that O. binervulum can be resurrected for plants belonging to the grade annotated here as O. strictum 3 (containing, e.g., the specimen from Austria: Upper Austria, Hochschwab Mts, Rinnerhütte, coll. Köckinger 15250, isolate Ot1703, Fig. 17J View Fig ). The morphology of these plants agrees with two available syntypes from Austria and Italy ( Figs. 19 View Fig , 20 View Fig ), although unfortunately, both syntype specimens and the recent Austrian collections from Austrian Alps rather represent the smaller expressions while all robust, morphologically distinct plants originate from northeast-Asian collections. Orthothecium binervulum was moreover described from four different localities in the peripheral ranges of the Alps, although in all cases from markedly less cryophilous conditions and in all cases from calcareous substrates, in contrast to the crystalline rocks of the Hohe Tauern Mts in the close proximity of Pasterze glacier at the type locality of O. strictum (H. Köckinger, pers. comm.). Whether the match with habitat and the slight morphological differentiation is fully consistent across the distribution range of the species, needs to be confirmed, however it is noteworthy that the Asian barcoded collections of O. strictum 1 also mostly originated from non-calcareous areas.

With respect to the enormous morphological plasticity within O. strictum 2–4 lineages and the relatively small amount of molecularly barcoded material, it would be premature to suggest any taxonomic consequences from the molecular resolution within O. strictum s.l., as the observed differences could not be used for practical identification. For example, the leaf shape seems to form a continuum among the lineages ( Fig. 17 View Fig ), although the specimens from clade 1 ( Fig. 17B–F View Fig ) have rather small, narrow-leaved plants with leaves lanceolate, 0.6–1.4× 0.2– 0.4 mm. Representatives of clade 2 ( Fig. 17G–I View Fig ) have mostly longer and relatively narrow-leaved plants with leaves 1.4–1.8× 0.3–0.6 mm, approaching in leaf length to plants of the grade 3. The most common grade (polytomy) 3 ( Fig. 17J–R View Fig ) is especially variable: some plants comprise phenotypes with ovate-lanceolate leaves ( Fig. 17J–K View Fig ) 1.1–1.4× 0.45–0.50 mm, similar to the type material of O. binervulum ( Figs. 19 View Fig , 20 View Fig ), while others comprise plants with leaves very variable in shape and size ( Fig. 17L–R View Fig ): ovate-lanceolate, triangular-lanceolate and lanceolate, 1.1–1.7× 0.3–0.6 mm. Four specimens of clade 4 ( Fig. 17S–V View Fig ) are also extremely variable, comprising plants with the smallest and the largest leaves ( Fig.17S & V View Fig ), as well as a fertile specimen with falcate-secund leaves ( Fig. 17U View Fig ); leaf size in this clade is the most variable, 0.9–2.2× 0.3–0.6 mm ( Fig. 17S–V View Fig ).

The lectotypification of O. binervulum requires special attention, as Molendo in his original description ( Lorentz, 1864) mentioned that the leaves of O. binervulum are shorter than leaves of O. strictum , whereas Limpricht (1895) mentioned that O. binervulum has larger leaves, up to 2(–3) mm long, matching our interpretation of the types. It is likely that Limpricht’s opinion convinced many later authors ( Brotherus, 1925; Podpěra, 1953) to accept this taxon.

There are morphotypes of O. strictum that have some aspects of O. intricatum , including poorly expressed recurved leaf margins, very narrow leaves, but the most unusual plants were found in Yakutia, in the foothills of Mramornaya mountain, a giant marble monolith piece, and one of two areas where Andreaeobryum macrosporum Steere & B.M. Murray was found in Eurasia ( Ignatov et al., 2018). Several specimens were collected in very close proximity; they were named in the field as Hygrohypnum luridum due to falcate-secund leaves and numerous sporophytes. However, closer examination revealed undifferentiated alar cells, a dioicous sexual condition, and axillary rhizoids, and molecular data pointed at an affinity with Orthothecium strictum . It is noteworthy that curved and inclined capsules are unique in Orthothecium : its generic name refers to straight, erect capsules which are often present in European collections of O. rufescens and O. intricatum .