Gymnomitrion schusteranum Konstant., D.

Konstantinova, N. A., Long, D. G., Mamontov, Y. S. & Vilnet, A. A., 2021, Gymnomitrion schusteranum (Gymnomitriaceae), a new species from the Sino-Himalaya, Arctoa 30 (2), pp. 149-158 : 150-152

Gymnomitrion schusteranum Konstant., D. G.Long, Mamontov & Vilnet, sp. nov. Figs. 2–5 .

Diagnosis. Plants blackish brown, middle-sized, with leaves 1.5–2 times as long as wide, deeply divided into two clearly unequal lobes with recurved margins of both lobes and sinuses and characterized by the presence of a clear vitta, 2–3(–4)-layered at the base, bifurcating approximately in the middle of the undivided part of the leaf and reaching the middle of the lobes.

TYPE. CHINA. Yunnan Province, Gongshan County, Cikai Zheng, east slope of Gaoligong Shan, Nu Jiang (Salween) catchment, Yipisaka Lake at head of Pula He valley, 2.2 km SSE of tunnel , 27°45’12.4”N, 98°27’36.4”E, alt. c. 3455 m a.s.l., 12 August 2006, D.G. Long 35728 ( KPABG – holotype ; E, KUN, CAS, MO, MHA – isotypes) .

Etymology: The species is named after Rudolf M. Schuster, one of the world’s foremost bryologists over many decades, who made an immense contribution to the study of the diversity, phylogeny and taxonomy of liverworts.

Description. Plants when dry blackish, when moist from pale green (uppermost apices) and dark chocolate brown in upper parts of shoots to blackish brown below, with main shoots ca. 0.6 mm wide and branches ca. 0.4 mm, up to 20–25 mm long, branching both dorsal intercalary ( Andrewsianthus -type) and ventral intercalary, mostly at base of shoots. Cells on dorsal side of stem almost isodiametric, of irregular form, rounded-rectangular or rounded-triangular, thick-walled, small, ca. (12–) 15–17 µm. Stem cross-section ( Fig. 3I , 4D ) elliptical, on main shoot 200–225 µm high and 260–280 µm wide, with distinct cortex of (3–)4–5 layers of dark brown thickwalled, small, almost isodiametric (or elongate along the margin) cells ca. 7–8(–10) × (10–)14–17(–20) µm and with slightly larger and paler outermost layer of cortical cells. Cells of medulla distinctly larger, thin-walled with distinct trigones, ca. 10–15 × 20–25 µm. Stem surface smooth ( Fig. 4D ), but in places appearing papillose through the leaf base cells bearing dome-like projections ( Fig. 3I ). Rhizoids colorless, 10–11 µm wide, absent on leafy shoots and occurring sparsely only on single small leaved stolon-like shoots arising from rhizome-like leafless structures at base of plants. Leaves ( Fig. 2C, E–G, I ; 5C, E ) when dry slightly falcate, in Long 35728 clearly directed to the ventral side ( Fig. 4A ), straight with dorsal lobe partly suberect spreading, transversely inserted, imbricate, hiding and sheathing the stem, slightly decurrent both dorsally and ventrally ( Fig. 4C ), subovate, variable and smaller on upper parts of shoots, bifid, distinctly longer than wide, 600–700(–900) µm wide near the base, slightly tapering upwards, 1000–1350(–1400) µm long on main axes, the length/width ratio (1.4–)1.5– 1.7(–2), slightly smaller on branches where leaves are 550–650 × 950–1100 µm; leaves deeply divided by narrow sinus rounded at base, up to (0.5)0.6–0.7 leaf length, into two distinctly unequal subulate lobes with more or less distinctly reflexed margins and sinuses. Lobes cuspidate, ending in 1–2 superposed almost isodiametric cells ca. 8–10 × 8–10 µm ( Fig. 3C, I ). Vitta massive, 2–3(–4) layers thick ( Fig. 3F, G, H, J ), bifurcate near the base of lamina, just 5–7 cells under the base. Vitta cells (10–) 12–15 × (20–)25–50 µm, very variable, thin walled with small to minute trigones. Cells on margins of leaf lobes variously oriented and elongated perpendicular to the margin below, 5–7 × 8–10 µm measured along margins, (6–)7–8 × 8–10 µm in lobes and slightly increasing downwards, 8–10(–12) × 10–15 µm, slightly obliquely elongated towards the vitta, with small to large trigones and a more or less distinct middle lamella in cell walls. Cells at the very base of leaves near the margins thick-walled with lumen 5–8(–10) µm and walls between two cells 4– 5 µm with distinct deeper colored lamella. Above the angular thickenings, both inner and outer surfaces of leaves bear at places (especially over vitta) low, domelike, indistinct to more or less distinct projections (papillae) which can be seen only in leaf cross section ( Fig. 3E, F, G, J ) due to its high transparency. Plants dioicous. Male shoots have been found only in the Indian specimen ( Iwatsuki B9), while the female ones only in the Chinese specimen ( Long 35728). Androecia intercalary, composed by 2–4 pairs of bracts, 1–2-androus; male bracts ( Fig. 5A, D, F, G ) almost not differing from leaves in length and width, deeply concave, with relatively short sinus (0.28–0.38 of the length) and saccate basal portion; antheridial stalks biseriate, 240–310 µm long. Gynoecia terminal; female bracts erect ( Fig. 2A ), mostly not differing from leaves in length, but comparatively wider, deeply concave, with relatively short sinus (0.28– 0.43 of the length). Perigynium and perianth lacking, shoot calyptra translucent ( Fig. 3D ), up to 700 µm long. Capsule globose ( Fig. 2A ), elaters 2-spiral, 7–10 µm in diam. Spores yellowish brown, 10–12 µm in diameter.

Differentiation. In general appearance, Gymnomitrion schusteranum resembles G. revolutum in size, col-or, sheathing of base leaves, and the revolute margins of leaves and sinuses. However, the new species is characterized by a set of features that immediately distinguish it from both this and other species of the genus. In particular, none of the other species of the genus known to us has such a clear leaf vitta (cf. Damsholt, 2002, Plate103 fig. 5). The elongated leaves with a length exceeding the width by 1.5–2 times and a very deep sinuses up to 0.5– 0.7 leaf length are also characteristic. In size, color, and shape of leaves deeply divided into two lobes and having a distinct vitta, the new species resembles representatives of the genus Herbertus Gray at first glance. However, the absence of underleaves serves to immediately distinguish G. schusteranum from Herbertus species even in the field.

Additional studied specimen. INDIA. West Bengal, near Sandakphu, Darjeeling area, 11,600–11,900 ft, 26 April 1965, Z. Iwatsuki et al. B 9 (MO, MHA – paratypes).

Distribution. To date this species is known only from China (Yunnan Province) and India (State of West Bengal). However, based on the two known locations that are remote from each other by about 1000 km, we can assume a much wider distribution of the species. Undoubtedly more extensive sampling in the Himalaya will lead to further localities for this species.

Ecology. The type specimen of Gymnomitrion schusteranum was collected on the eastern (Chinese) side of the Gaoligong Shan, the dividing range between Yunnan and Myanmar, within the catchment of the Salween (Nu Jiang) River at a height of 3455 m. The area is dominated by somewhat undisturbed Abies / Rhododendron forest up to approximately the altitude of the collection where the Abies trees had become relatively few (see image) and the steep rocky slopes were dominated by dense thickets of bamboo (foreground in image) and Rhododendron shrubberies. Around the lake shore were low rock outcrops where the type specimen was collected in a deep shady, moist rock cleft. The species associated with Gymnomitrion schusteranum are the mosses Andreaea rigida Wilson ex Mitt. , Atractylocarpus alpinus (Schimp. ex Milde) Lindb. and Sanionia uncinata (Hedw.) Loeske , and the liverworts Diplophyllum taxifolium (Wahlenb.) Dumort. , Pseudolepicolea trollii (Herzog) Grolle & Ando , Scapania contorta Mitt. , S. ferruginea (Lehm. & Lindenb.) Lehm. & Lidenb. , Schistochilopsis setosa (Mitt.) Konstant. , Solenostoma appressifolium (Mitt.) Váňa & D.G.Long, S. ohbae (Amakawa) C.Gao, and S. subacutum (Herzog) Váňa, Crand.-Stotl. & Stotler. The paratype specimen of Gymnomitrion schusteranum was collected on a cliff shelf near Sandakphu in Darjeeling District, State of West Bengal (India), at a height of ca. 3530–3630 m. Associated liverworts are Anastrophyllum assimile (Mitt.) Steph. , Bazzania sp. , Blepharostoma trichophyllum (L.) Dumort., Cololejeunea sp. , Gymnomitrion sp. , Riccardia sp. , and Scapania ornithopoides (With.) Waddell. The distance between the two known localities of the species is about 1000 km.

Figures

Fig. 2. Gymnomitrion schusteranum. A – female shoot apex with gynoecium and sporophyte. B – sterile part of shoot (ventral view). C, E–G, I – leaves. D – part of the leaf lamina. H – cells of the leaf lobe near vitta. J – cells of the leaf base. K – cells of the leaf lobe in vitta area. All from holotype, Long 35728 (KPABG).

Fig. 3. Gymnomitrion schusteranum. A, B, C – innermost female bracts. D – shoot calyptra. E–H, J – leaf cross sections. I – stem cross section. All from holotype, Long 35728 (KPABG).

Fig. 4. Gymnomitrion schusteranum. A – dry habit. B, E – leaf lobe apices. C – part of shoot showing leaf insertion (ventral view). D – stem cross section. F, H – cells of leaf lamina below sinus. G – cells of leaf margin near the leaf base. All from holotype, Long 35728 (KPABG).

Fig. 5. Gymnomitrion schusteranum. A, B – parts of the same male shoot (ventral view). C, E – leaves. D – parts of a male shoot. F, G – male bracts. H, J – parts of leaf lobes. I – leaf lobe apex. All from paratype, Iwatsuki B9 (MHA).