Nardia pacifica Bakalin, Bot. Pacif.

Nardia pacifica Bakalin, Bot. Pacif. View in CoL 5(2): 45, 1,

2.2016. Fig.2 View Fig .

Shoots are 0.9–1.2 mm wide and to 12 mm long; stem straight to slightly flexuose, with both lateral and ventral intercalar branches and intercalar stolones and small-leaved branches; rhizoids sparse, mostly at base of plant or numerous at base of perigynium. Stem cross-section wide elliptical, 200–210×230–240 µm, cells of cross-section not differentiated, thin-walled, with small but distinct trigones, mostly large, 20–25×25–35 µm, with admixture of small cells just 12–15 µm as wide as long. Leaves obliquely inserted, plane or slightly concave, light green to light warm brown (in Alaska) and rather pellucid at base and in the middle but with upper parts along margins sometimes brownish to red brownish, especially in the upper parts of shoots, suborbicular to obliquely trapezoidal, widest below the middle, 600–700 µm wide and 500–650 µm long, divided to 0.2–025(–0.3) of its length by obtuse, crescending to V-shaped sinus, lobes uneven, mostly obtuse, subacute or rounded. Underleaves distinct, large, lanceolate, 100–150×200–350 µm, spreading, triangular, with apex almost straight. Cells thin-walled, subisodiametric, with distinct, relatively large trigones, (17–)19–22(–25)×(20–)22–28(–30) µm in the middle of leaves and 25–30×30–45 µm near the base, where cells often are bistratose in 2–3 rows. Oil-bodies long persistent, homogenous, glistening, 2–3 per cell, rounded, 5–6 µm in diameter or ellipsoidal, 5×9 µm.

Dioicous. Androecium consists of 3–5 pairs of bracts that are slightly larger, wider and more concave than leaves, ca. 700–800 µm wide and 500–550 µm high, with two antheridia that have two-seriate stalks.

Female bracts lager than leaves, 900–1000 µm wide and 800 long, 3 pairs on large fleshy stem perigynium that is ca. 1000 µm long and ca. 600 µm wide, with numerous rhizoids on ventral side, especially at base. Perianth very short, completely hidden among the bracts placed at the tip of perigynium, mouth of perianth crenulate, consists of elongated, slightly protruding and expanding to the upper end of cells ca. 6–10×(13–)15–29 (–22) µm.

Capsule dark brown, ovoid-cylindrical, 450 × 600 µm, capsule walls 2 layers, epidermal cells with nodular thickenings ca. 1.5 as thick as inner walls, with 5–7 annular to semiannular bands. Elaters 8–10 µm wide, with bands 2.5–3.5 µm wide. Spores brown, finely papillate, 12–14 µm ( Fig. 2 View Fig )

Variation and differentiation. In general both Caucasian and Alaskan plants fit well to the description of the species. Plants from the Caucasus differ slightly in presence of intercalary ventral stolones and small-leaved shoots, which is not mentioned by the authors of the species description. In addition, Caucasian plants in general have a slightly smaller sinus and smaller midleaf cells, the values of which are closer to the lower limit described for the type. Plants from Alaska are slightly smaller in size, with a shoot width no more than 1 mm and are mostly more deeply brown colored with margins of leaves red-brown in upper leaves in some plants.

The differences between Nardia pacifica , N. japonica and N. lescurii are described in detail by Bakalin & Klimova (2016) and briefly consist in the smaller size of N. japonica and the larger size of N. lescurii compared to N. pacifica , as well as the structure and size of the oil bodies that are smooth in N. pacifica but coarsely granulate in N. japonica and more numerous and finely granulate papillose in N. lescurii . From Barbilophozia sudetica occurring mixed with Nardia pacifica in Caucasus Nardia pacifica differs in smaller size, color and presence of distinct large underleaves.

Ecology. Both in the Caucasus and Alaska, the species was collected on moist sandy soil in late snow bed, mixed with arctomontane species typical for such habitats, e.g. Anthelia juratzkana , Barbilophozia sudetica, Pleurocladula albescens. In both specimens the species is scattered among other bryophytes. The type specimen was collected on moist boulder in alpine belt. Apparently, we can characterize the species as a hygromesophyte.

Distribution. Currently, the species is reliably known from the Caucasus, the Far East of Russia and Alaska. Bakalin & Klimova (2016) presumably referred to Nardia pacifica specimens from Karelia Republic (European part of Russia) and Washington State ( U.S.A.) which they studied without oil-bodies and also suggested that the records of Nardia japonica for Timan, Komi Republic of Russia (Schljakov, 1981) and Alaska ( Hong & Váňa, 2000) could also be attributed to Nardia pacifica . Our data confirm the wide distribution of the species, and taking into account the discovery the species in the Caucasus, even show a much wider distribution of the species than was supposed by the authors of its description ( Bakalin & Klimova, 2016). Based on these data we can state that the species has an arctomontane suboceanic, almost circumpolar distribution.

DISCUSSION AND CONCLUSION

Bakalin & Klimova (2016) clarified the morphological concept of N. japonica including a critical revision of different treatments of the species and described N. pacifica based on morphological differences of this species from N. japonica . Considering, however, that one of the main differences between N. japonica and N. pacifica lies in features of the oil bodies, which have not been preserved in the type as well as in a majority of herbarium specimens, the molecular genetic study of N. japonica specimens from the type or close to its locality is of particular importance. In this work, we were able to sequence DNA and identify molecular similarities in the isotype and two more samples of N. pacifica , however an obvious disadvantage of both Bakalin & Klimova (2016) and our studies is the lack of sequenced specimens of N. japonica . Unfortunately, we could not find a suitable material of this species for sequencing. Therefore, until it is possible to study live material and obtain sequences of N. japonica from the type or close to the type locality, all conclusions on taxonomical status and volume of the latter species are preliminary.

Differences in ecology of these two species also remain unclear. So Nardia pacifica is characterized by Bakalin & Klimova (2016) as “ unlike to the latter ( N. japonica , N.K.), N. pacifica prefers well formed bryophyte synusia”. However “fine soil along stream, stones near streams covered with thin soil” that is characteristic for Nardia japonica do not contradict occurring of “well formed bryophyte synusia”. In many specimens preserved in KPABG which we earlier referred to N. japonica , the species occurs mixed with other bryophytes, similar to sequenced specimens of N. pacifica both from Alaska and the Caucasus where the latter species occurs in stiff mats of other liverworts on grained sandy soil. All this leaves open the question of the distribution of these species, particularly it is not clear to which species the numerous records of N. japonica from the European and Asian parts of Russia belong. For a more or less correct solution to this issue, it requires the study of living material and/or at least selective DNA sequencing of specimens.

The genus Nardia occupies an isolated position and was recently allocated to a separate subfamily Nardioideae Váňa in the family Gymnomitriaceae (Váňa et al., 2014) . The genus was placed in this family as a result of modern molecular phylogenetic studies of the largest families of previously accepted suborder Jungermanniinae – Lophoziaceae , Scapaniaceae , Gymnomitriaceae and Jungermanniaceae (Vilnet et al., 2010, 2011). These studies (l.c.) included only three species of Nardia . Later, Shaw et al. (2015) tested nine species presented by twelve specimens and supported the results obtained earlier (l.c.) but stressed that the interspecific relationships within the genus remain unclear. The inclusion in our study of three N. pacifica specimens did not change the topology obtained earlier. Particularly, four specimens identified as N. geoscyphus turned out to locate in different clades. A comparative morphological study of the sequenced samples is necessary to decide which of them belong to the Nardia geoscyphus and to which species belong the samples from the second clade named as well Nardia geoscyphus . At this stage we can only support the conclusion of Shaw et al. (2015) that “expanded population level studies are needed to resolve species level relationships and evolutionary groups within the genus”.