Gymnomitrion sichuanicum Bakalin et Vilnet, 2022

Bakalin, Vadim, Vilnet, Anna, Long, David, Klimova, Ksenia, Maltseva, Yulia, Nguyen, Van Sinh & Ma, Wen Zhang, 2022, On two species of Gymnomitrion (Gymnomitriaceae, Marchantiophyta) in the Eastern Sino-Himalaya, Phytotaxa 533 (2), pp. 117-136 : 123-125

Gymnomitrion sichuanicum Bakalin et Vilnet sp. nov.

Description: Plants blackish brown, slightly glistening, sometimes with discolored leaf margin (but never erose) making patches paler in color (grading to greyish); forming loose to dense patches; rhizomatous base well-developed, originating as geotropic stolons from plagiotropic normally leaved branches, sometimes bearing scale-like leaves; freely rhizogenous, freely branching, giving rise to sterile and fertile branches; leafy branches varying in size, mostly erect, rarely creeping (and then producing erect intercalary branched or plagiotropic stolons), from 250–300 to 500–700 μm wide, 1000–2000 μm long; clavate, larger branches with cupped and ventricose leaves as if containing antheridia; larger branches dorsiventrally compressed, ribbon-vermicular. Rhizoids abundant in rhizomatous part, rare on plagiotropic branches and virtually absent in erect branches, colorless to brownish and grayish. Stem freely branched in rhizogenous part, virtually unbranched in erect shoots and sparsely producing ventral leafless stolons in creeping leafy branches; orbicular in cross section, 110–140 μm in diameter, outer cells larger than inner and with colorless walls that look like a hyalodermis, cells have large trigones and thickened walls, 10–18 μm long and 8–12 μm wide, inner cells with brown-rusty colored cell walls, thin-walled or at least thinner than outer, 7–16 μm in diameter. Leaves densely imbricate, concave to cupped, sometimes distinctly ventricose (then similar to male bracts, but no antheridia found); transversely inserted, transversely oriented, shortly decurrent on both sides, with plane to slightly to evidently recurved margin, mostly evident in lower half of the leaf, varying in shape: from transversely ellipsoidal and narrowly trapezoidal (smaller) to suborbicular and ovate (larger), leaves commonly lacerate or plicate when flattened on a slide, mostly 350–560 × 330–530 μm with larger leaves to 600 × 550 μm, divided by semicrescentic (rarely widely V-shaped) sinus descending to 1/15–1/9 of leaf length into two acute to obtuse (never rounded) lobes. Cell size strongly varying across leaf: near base, oblong 20–30 × 10–15 μm, thin-walled, with moderately sized concave trigones and occasionally occurring intermediate thickenings; in midleaf 10–15 × 7–12 μm, with slightly thickened to thin walls with large concave to convex trigones; in lobe apices subisodiametric, ca. 7–10 μm in diameter, thin-walled, with concave trigones; in leaf margin near leaf base oblong, 10–15 × 7–11 μm, thick-walled, with concave trigones; cuticle smooth throughout; trigones and cell walls always colorless, while content of the cell varies in color from colorless and greenish to brown (this determines coloration of whole plant); oil bodies in midleaf cells smooth-surfaced, homogenous, 2–3 per cell, relatively small, 2–3 μm in diameter to oblong 3–4 × 2–3 μm. Dioicous? (androecia not seen). Female plants with sequential unfertilized terminal gynoecia with 1–3 subfloral innovations; female bracts similar to larger leaves. Other generative features unknown ( Figs 2 , 3 ).

Holotype:— CHINA. Sichuan Province: Kangding airport area, SW-facing gentle slope of the range, covered with communities like hummocky tundra with low Rhododendron and Pentaphylloides .Crusts in open and dry frosty weathering spot, 4474 m a.s.l., 30°07’1.2”N 101°46’40.8”E, 14 October 2017, V.A. Bakalin & K.G. Klimova China-45-2-17 (VBGI) (with tiny admixture of Isopaches decolorans . ITS1-2: MW829523 , trn L-F: MW841070 .

Paratypes:— CHINA. Sichuan Province: Kangding airport area, SW-facing gentle slope of the range, covered with communities like hummocky tundra with low Rhododendron sp. and Pentaphylloides sp. Crusts on open and dry frosty weathering spot, 4474 m a.s.l., 30°07’1.2”N 101°46’40.8”E, 14 October 2017, V.A. Bakalin & K.G. Klimova China-45- 1-17 (VBGI) ( Anthelia juratzkana dominates in the specimen); the same 4335 m a.s.l., 30°06’39.6”N 101°46’22.8”E, 14 October 2017, V.A. Bakalin & K.G. Klimova China-43-1-17 (VBGI).

Differentiation: When collected, the specimens were preliminarily named as Marsupella sprucei . Indeed, the short, clavate, loosely dorsiventrally compressed shoots with imbricate leaves arising from rhizomatous base resemble M. sprucei , although different in as fundamental a feature as total absence of perianth. The leaf shape is somewhat similar to Marsupella apiculata Schiffner (1903: 249–252) (but no discolored thin-walled cells along leaf margin are present) or even M. condensata (Ångström ex Hartman (1871: 128)) Lindberg ex Kaalaas (1893: 420). The absence of a perianth suggested that it should be placed in Gymnomitrion , as was later confirmed by molecular analysis. Gymnomitrion sichuanicum provides evidence of similarity with Marsupella sprucei not only in morphology, but also in ecology: the species is growing on fine-grained soil of frosty weathering spots in heathlands with very scattered vegetation. It forms patches incrusted with mineral soil. The original specimens are quite large and collected in two sites ruling out the possibility of the taxon being an incidentally occurring dwarf modification of that species (avoiding the suggestion that well developed plants could be similar to the bulk of taxa previously referred to the genus Apomarsupella Schuster (1996: 79) found nested within Gymnomitrion , cf. Shaw et al. 2015). The genetic relatives of the species include Gymnomitrion revolutum ( Nees 1836: 419–420) Philibert (1890: 34) and G. parvitextum ( Stephani 1901: 165) Mamontov, Konstantinova & Potemkin (2018 [2017]: 88); those species never produce short clavate shoots in patches incrusted with soil and have a deeper, leaf sinus, never semi-crescentic and therefore could hardly be mistaken for the two aforementioned taxa. Moreover, both are epilithic taxa, not epigeal. Meanwhile, it is worth mentioning that the leaf cell network is quite similar to G. revolutum in the thin cell walls and commonly concave trigones. Genetically the most closely related species is Gymnomitrion africanum described from African Mt. Kilimanjaro (1901, leg. Uhlig, G-00046686/10873, lectotype selected by Váňa 1985). The latter species (based on the lectotype) is different from G. sichuanicum in its gibbous sinus descending to 1/4–1/3(–2/5) of the leaf length and rounded leaf lobes (versus sinus descending to 1/15–1/9 of leaf length and lobes acute to obtuse), and also in stem cross section, with outer cells with very thick walls and somewhat smaller than inner cells (versus distinctly larger, hyalodermis-like cells, but with thick walls in G. sichuanicum ).

Ecology and expected distribution: Despite the species being collected only three times from two neighboring sites, it is possible to describe its ecology in some detail, also taking into comparative consideration the data on the ecology of Marsupella sprucei . Gymnomitrion sichuanicum grows in highland heathlands above 4000 m a.s.l., with sparse vegetation, where Rhododendron Linnaeus (1753: 392) and Pentaphylloides Duhamel (1755: 99) patches form the shrubby clumps. Sedge patches associated with Scapania sichuanica Bakalin & Vilnet (2019: 139) and Poeltia campylata Grolle (1966a: 280) and hygrophilous mosses are typical inhabitants of wet places near streams. The remaining dominant area, however, is almost free of vegetation and comprises gravelly barrens with spots of fine-grained soil of cryogenic origin (frosty weathering spots) with scattered cushions of xerophilous or xero-tolerant species. Gymnomitrion sichuanicum occurs mostly in pure patches, although at the margin in one patch (holotype) a scanty admixture of gemmiparous plants of Isopaches decolorans ( Limpricht 1880: 316) Buch (1932: 288) was observed. The other specimen (China-45-1-17) comprises Gymnomitrion sichuanicum in an admixture with Anthelia juratzkana (Limpricht in Cohn (1877: 289)) Trevisan (1877: 416). The latter associate, along with the theoretically expected water circulation in frosty weathering spots, suggest temporary moistening of the patches, probably in the spring snow-melting season, while at the time of collection (middle October) the crusts were completely dry.

The gentle slope described above is intermingled with extensive rocky outcrops which support some other bryophytes including xerophilous liverworts. The same area is the type locality for Plagiochila xerophila Bakalin & Vilnet (2020: 127) described previously from dry cliffs, where grew nearby the peculiar Sino-Himalayan Gymnomitrion sinense (Bakalin & Vilnet 2020) . Plagiochila xerophila is probably one of the most xerophilous representatives of Plagiochila ( Dumortier 1831: 42) Dumortier (1835: 14) in Asia, which may help to illustrate the environments surrounding the type locality of Gymnomitrion sichuanicum . The climate characteristics and natural environments were discussed previously (Bakalin & Vilnet 2020), but here adding only key characteristics, based on information from Table 1 : 1. The area is 500 m above the timberline (the nearest forests are slightly more than 10 km to the southeast from the collecting localities), 2) annual mean temperature is slightly negative (–2.7), with the coldest month mean temperature –17°C. The total amount of precipitation is 775 mm per year, with 55% falling in the wettest summer quarter, for the driest winter quarter the precipitation is only 16 mm per quarter. Therefore, the climate has pronounced highland monsoon characteristics with a cold, dry winter. These characteristics may be similar to the climate in the area of distribution of Marsupella sprucei . Although the latter is largely distributed in areas with oceanic/suboceanic climates, the character of the growing season is somewhat similar (wet), whereas the winter is much dryer in Sichuan (versus, e.g., in suboceanic NE Asia), and negative temperatures are associated with the absence of snow cover that seems to be suitable for many Gymnomitrion , but not so for Marsupella Dumortier (1822: 114) . The collecting area is on the southeast edge of the Tibetan Province of the Irano-Turanian floristic region (cf. Chang 1981, Takhtajan 1986) and the collected species likely belongs to the Tibetan element and may be much more widely distributed along the Tibetan highlands and probably northern slope of the Himalaya. The same was previously suggested for Plagiochila xerophila (Bakalin & Vilnet 2020) .

Figures

FIGURE 2. Gymnomitrion sichuanicum Bakalin & Vilnet:A, C—plant habit, dorsal view; B, D—plant habit, lateral view; E–L—leaves; M—stem cross-section. Scales: a—500 µm, for A–D; b—500 µm for E–L; c—100 µm for M. All from China-45-2-17 (VBGI).

FIGURE 3. Gymnomitrion sichuanicum Bakalin & Vilnet:A, B—plant habit, fragment, dorsal view; C–F—leaves. Scales: for A, B—500 μm, C–F—300 μm. All from China-4-2-17 (VBGI).