Odontoschisma dimorpha (Casp.) Heinrichs, K.Feldberg, Váňa & Schäf.

Mamontov, Yuriy S., Schäfer-Verwimp, Alfons, Feldberg, Kathrin, Vasilenko, Dmitry V., Legalov, Andrei A. & Perkovsky, Evgeny E., 2024, Hepatics from Rovno amber (Ukraine). 14. Lejeunea aristovii sp. nov. and Odontoschisma dimorpha from Belokorovychi, Ecologica Montenegrina 80, pp. 230-243 : 235-238

Odontoschisma dimorpha (Casp.) Heinrichs, K.Feldberg, Váňa & Schäf. -Verw. ( Figs. 3 , 4 ).

Type material: MB. Pb.1979/687 (Museum für Naturkunde, Leibniz Institute for Evolution and Biodiversity Science in Berlin; holotype) .

Additional specimens examined: Rovno amber: SIZK-Be-18 d, SIZK-Be-18e , SIZK-Be-18 f (Schmalhausen Institute of Zoology in Kiev). Baltic amber: GZG.BST. 22048 (Geoscientific Collections of the University of Göttingen, Germany).

Description: Shoots greyish or yellowish, prostrate, creeping, up to 1.5 mm long and (0.13–) 0.25–0.44 mm wide, not branched. Stem straight to curved, not or slightly translucent, (70–)80–105 μm in diameter. Epidermis not hyalodermatic, cells hardly visible, square or mostly short rectangular, 11.2– 17.8 × 10.5–14.5 μm. Rhizoids not seen. Leaves with straight insertion line, distinctly succubous, subtransverse to very oblique or almost horizontal, reaching or nearly reaching the dorsal midline ( Fig. 3A ), neither dorsally nor ventrally decurrent, remote to contiguous in the same shoot, erect to spreading or leaning on the stem, usually somewhat elevated to the dorsal side, slightly to rather distinctly concave (in dorsal view), variable in size and shape, sometimes reduced, scaly, if well-developed ovate to ovate-oblong to rectangular, ca. (70–)147–287 μm long (including lobes), (86–)135–245 μm wide, ca. 0.81– 1.21× as long as wide, widest in or slightly below the middle and narrowing towards apex, not or slightly narrowing towards base, subsymmetric, margins entire, bilobed to 0.15–0.33 the length, sinus acute or rectangular, with rounded angular base, lobes equal in size, sometimes ventral one slightly larger, directed forward or mostly ± converging, broadly triangular to triangular, (2–)3–6 cells wide at base, apex acute, usually formed by a single long triangular cell, sometimes by two uniseriate cells, dorsal and ventral margin strongly arcuate or almost straight or somewhat angulate ( Fig. 3A ). Cells hardly visible, 14.9–18.2 µm long × 13.1–16.2 μm wide, with strongly incrassate walls. Underleaves, asexual reproduction, and gametangia not observed.

Comparison: Odontoschisma dimorpha has seen significant taxonomical changes over the years. First it was described as Jungermannia dimorpha Casp. , based on a single specimen with androecia, and then it was transferred to the family Cephaloziellaceae as more fossil material became available. Grolle included it first in Cephaloziella (Spruce) Schiffn. ( Grolle 1980, as Cephaloziella dimorpha (Casp.) Grolle ) and later in Cylindrocolea R.M.Schust. ( Grolle & Meister 2004, as Cylindrocolea dimorpha (Casp.) Grolle ). Among the relatively rare fossils of Jungermanniales , O. dimorpha became the most frequently found, with ca. 19 inclusions in Baltic and ca. 15 in Bitterfeld amber. This allows a comparatively detailed assessment of the considerable morphological variability. The plants grow in mats of creeping and ascending shoots, the latter occasionally bearing multicellular, deeply bifid underleaves ( Feldberg et al. 2017). The presence of these underleaves as well as the occurrence of ventral-intercalary branches, isodiametric leaf cells with equally thickened walls, and an androecium on an elongated branch align the fossil species with extant representatives of the pantropical Iwatsukia which is now treated as a section of Odontoschisma ( Aranda et al. 2014; Gradstein et al. 2014; Gradstein & Ilkiu-Borges 2015). The plants studied here generally resemble the plants of O. dimorpha illustrated in Grolle & Meister (2004: 71, plate 3a, 3b, as Cylindrocolea dimorpha ) and Feldberg et al. (2017: 150, fig. 2a, 2b). For comparison a shoot fragment from Baltic amber (GZG.BST.22048) is pictured in Fig. 4D, 4E . The leaves strongly resemble those of the Rovno amber fossil and the shoot is also tapering into a flagella-like part with tiny reduced leaves. The leaf insertion that varies from nearly transversal to nearly horizontal is typical for the species. In Grolle & Meister (2004) and Feldberg et al. (2017), leaves of O. dimorpha were characterized as having a sinus descending 0.3–0.6 of the leaf length, whereas in the shoots studied here the leaves are bilobed to only 0.15–0.33 of the length. However, in the specimen GZG.BST.22048 ( Fig. 4E ) and in the shoot imaged in Feldberg et al. (2017: 150, fig. 2a) some leaves are bilobed up to 0.2 the length and are very similar to the leaves of the Rovno plants ( Fig. 3A, 3D ). Therefore, the Rovno plants fall rather well within the morphological range of the species. In the Baltic plants, the walls of the leaf cells are evenly thickened or becoming slightly thicker towards the corners, sometimes thin-walled, while in the Rovno plants the leaf cell walls are strongly incrassate, but also becoming thicker towards the corners ( Fig. 3F ). Another character that aligns it with typical O. dimorpha is the tapering shoot with the leaves becoming successively smaller and more distant ( Fig. 4A, 4D ). Another fossil species similar to some very small, creeping or tapering shoots of O. dimorpha is Cephalozia veltenii T.Katag. from Baltic amber ( Katagiri 2015). The species has tiny leaves in relation to its robust stem and is differentiated by the presence of a stem hyalodermis.

Additional photos: MB.Pb.1979/687 (Künow amber collection 144a): type from Baltic amber ( Feldberg et al. 2017: 149, fig. 1a–d); Gröhn 2038: mat with creeping and ascending shoots from Baltic amber ( Feldberg et al. 2017: 150, fig. 2f); GZG.BST.21958: ascending shoot with underleaf from Bitterfeld amber ( Feldberg et al. 2017: 150, fig. 2a–d), rather similar to the new fossil.

Figures

Figure 3. Odontoschisma dimorpha (photo): A, D – habit, dorsal aspect (parts of the same shoot). B – shoot, ventral aspect. C – shoot, dorsal aspect. E – close-up of the area selected in Fig. 3A. F – close-up of the area selected in Fig. 3B. G – close-up of the area selected in Fig. 3C. A, D, E from SIZK-Be-18d; B, F from SIZK-Be- 18e; C, G from SIZK-Be-18f.

Figure 4. Odontoschisma dimorpha (line drawings and photo): A–C – graphic reconstructions of Fig. 3A–D. D, E – habit, lateral aspect (parts of the same shoot). A from SIZK-Be-18d; B from SIZK-Be-18e; C from SIZK-Be- 18f; D, E from GZG.BST.22048.