Hepatics from Rovno amber (Ukraine). 14. Lejeunea aristovii sp. nov. and Odontoschisma dimorpha from Belokorovychi

© 2024 The Author(s). This is an open access article distributed under the terms of the Creative Commons Attribution License (CC BY), which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. Hepatics from Rovno amber (Ukraine). 14. Lejeunea aristovii sp. nov. and Odontoschisma dimorpha from Belokorovychi YURIY S. MAMONTOV1,*, ALFONS SCHÄFER-VERWIMP2, KATHRIN FELDBERG3, DMITRY V. VASILENKO4,5, ANDREI A. LEGALOV6,7,8 & EVGENY E. PERKOVSKY9 1Polar-Alpine Botanical Garden-Institute, Kola Science Centre, Russian Academy of Sciences, Kirovsk 184256, Russia; https://orcid.org/0000-0003-3851-0738 2Mittlere Letten 11, 88634 Herdwangen-Schönach, Germany; https://orcid.org/0000-0002-2720-6055 3Department of Geobiology, University of Göttingen, Goldschmidtstraße 3, 37077 Göttingen, Germany; https://orcid.org/0000-0002-9431-7193 4Borissiak Paleontological Institute, Russian Academy of Sciences, Profsoyuznaya 123, Moscow 117997, Russia; https://orcid.org/0000-0002-4827-7290 5Cherepovets State University, Lunacharsky Prospect 5, Cherepovets 162600, Russia; 6Institute of Systematics and Ecology of Animals, Siberian Branch of the Russian Academy of Sciences, 630091 Novosibirsk, Russia; https://orcid.org/0000-0001-7347-8169 7Department of Ecology, Biochemistry and Biotechnology, Altai State University, 656049 Barnaul, Russia; 8Department of Forestry and Landscape Construction, Tomsk State University, 634050 Tomsk, Russia; 9Natural History Museum of Denmark, Universitetsparken 15, Copenhagen 2100, Denmark; https://orcid.org/0000-0002-7959-4379 * Corresponding author. E-mail: [email protected] Received 9 March 2024 │ Accepted by V. Pešić: 5 December 2024 │ Published online 26 December 2024. Abstract A study of Rovno amber has revealed two fossil leafy liverwort species of the genera Lejeunea and Odontoschisma (Marchantiophyta), which are new to the late Eocene flora of Rovno amber. One of these species, Odontoschisma dimorpha, is known from Baltic and Bitterfeld amber, whereas the other species, Lejeunea aristovii, is described here as new. Lejeunea aristovii differs from the most similar Paleogene species of that family, Cheilolejeunea latiloba, in the shape of its leaves and underleaves. Key words Fossil liverworts, taxonomy, Europe, Eocene, Jungermanniales, Porellales. Introduction Until now the leafy liverwort family Lejeuneaceae (Porellales) was represented in Rovno amber only by the extant genus Acrolejeunea (Spruce) Steph. (subfamily Ptychanthoideae) with the sole fossil species A. ucrainica Mamontov, Heinrichs & Schäf.-Verw. (Mamontov et al. 2013; Feldberg et al. 2021). This mainly epiphytic family includes ca. 1000 extant species across 72 extant genera and is the Ecologica Montenegrina 80: 230-243 (2024) This journal is available online at: www.biotaxa.org/em https://dx.doi.org/10.37828/em.2024.80.21 MAMONTOV ET AL. Ecologica Montenegrina, 80, 2024, 230-243 231 largest family of liverworts (Feldberg et al. 2021; Gradstein 2021) with a center of diversity in the humid tropics (Wilson et al. 2007; Feldberg et al. 2014). Recently, a specimen from the Zhitomir Region of Ukraine was studied and found to include an additional species of the Lejeuneaceae. In the shape of its leaves and underleaves this species resembles some extant members of Lejeunea Lib. (subfamily Lejeuneoideae), a large pantropical genus with about 200 to 300 species (Gradstein 2021; Lee et al. 2022). So far, Lejeunea fossils have only been found in Neogene deposits, specifically Miocene amber from the Dominican Republic (Reiner-Drehwald et al. 2012; Kaasalainen et al. 2018; Lee et al. 2017; Feldberg et al. 2021) and Mexico (Feldberg et al. in press). However, different divergence time estimates proposed a more ancient (Paleogene) age for Lejeunea – from 25.19‒34.15 Ma (Laenen et al. 2014) to 42.2‒52 Ma (Lee et al. 2020) and 51.59 Ma (Feldberg et al. 2014). Like other Lejeunea fossils, the plant studied here is sterile; moreover, only its dorsal side is available for observation, which makes comparison with extant Lejeuneoideae particularly problematic. The studied fossil has rather welldeveloped, deeply bifid underleaves, rounded to apiculate leaf lobe apices, and reduced or absent leaf lobules. These features distinguish this plant from the oldest fossils of the Lejeuneoideae, namely the Paleogene Cheilolejeunea latiloba (Casp.) Grolle (Grolle & Meister 2004; Feldberg et al. 2021) and Microlejeunea nyiahae Heinrichs, G.E.Lee, Schäf.-Verw. & A.R.Schmidt (Heinrichs et al. 2016), and indicate a close relationship to the genus Lejeunea. One more leafy liverwort discovered in the specimen from the Zhitomir Region of Ukraine is Odontoschisma dimorpha (Casp.) Heinrichs, K.Feldberg, Váňa & Schäf.-Verw., a species known from numerous collections from Baltic and Bitterfeld amber (Grolle & Meister 2004; Feldberg et al. 2017; see also the discussion on the presumed age of Bitterfeld amber (Eocene vs. Oligocene) in Dunlop 2010; Wolfe et al. 2016; Dunlop et al. 2018). This species is the only fossil representative of the widespread tropical-holarctic extant genus Odontoschisma (Dumort.) Dumort. (Cephaloziaceae, Jungermanniales), which includes 24 taxa (22 species + 2 subspecies) (Gradstein & Ilkiu-Borges 2015; Feldberg et al. 2016). Odontoschisma dimorpha is hypothesized to belong to the pantropical section Iwatsukia (N.Kitag.) Gradst., S.C.Aranda & Vanderp. with closest morphological similarity to the pantropical O. jishibae (Steph.) L.Söderstr. & Váňa (Feldberg et al. 2017). The record of this species increases the number of the species common to both Baltic and Rovno amber and brings the floras closer to each other. The descriptions and illustrations of the discovered taxa are provided below. Materials and methods Both studied species were found in the same amber piece SIZK-Be-18, which is a part of the Rovno amber collection of the Schmalhausen Institute of Zoology in Kiev. The age of Rovno amber is late Eocene, about 35–37 Ma (see discussion in Mitov et al. 2021; Perkovsky et al. 2007, 2010; Radchenko et al. 2021), the amber originates from the Volhynian Uplift (Ivanov et al. 2016; Chemyreva et al. 2024a). The piece was collected in a quarry 5 km south of Belokorovychi Village, Korosten District, Zhitomir Region; data on the amber biota from this region were recently summarized in Mamontov et al. (2024a) and Kazantsev et al. (2024). After primary preparation, the amber piece has a weight of 11.22 g and a spheroidal shape with a diameter of ca. 24 mm. Syninclusions consist of a stellate hair and several liverworts, including Jubula polessica Mamontov, J.J.Atwood & Perkovsky, Leptoscyphus davidii Mamontov, Ignatov, Vasilenko & Perkovsky, Nipponolejeunea solodovnikovii Mamontov, Schäf.-Verw. & Perkovsky, an undescribed species of Plagiochila (Dumort.) Dumort., and Radula oblongifolia Casp. (Mamontov et al. 2024a, 2024b, 2024c, 2024d). The shoots of the studied species were photographed using stereomicroscopes: an Olympus MVX10, equipped with a digital camera, an Infinity Lumenera 3-6 (Fig. 1A, 1E); a Nikon SMZ25, equipped with a digital camera, a Nikon DS-Fi3 (Fig. 1C, 2A–I, 3A, 3D, 3E–F); an Olympus SZX16, equipped with a digital camera, a Canon 1100D (Fig. 3B, 3C). To optimize visualization of the threedimensional inclusions, photomicrographs in Fig. 1–3 were combined from several optical sections using the focus stacking software Helicon Focus 8 (Kozub et al. 2008) or the focus stacking package EDF built into the NIS-Elements imaging software that controls the Nikon SMZ25. The final images were reconstructed in line drawings (Fig. 1B, 1D, 4A–C). For comparison a shoot fragment of Odontoschisma dimorpha from Eocene Baltic amber specimen GZG.BST.22048 was additionally studied. The specimen GZG.BST.22048 is housed in the HEPATICS FROM ROVNO AMBER. PART 14 232 Geoscientific Collections of the Georg August University of Göttingen, Germany. Photographic documentation of this specimen was done as described by Sadowski et al. (2021). The image (Fig. 4D) is composed of digitally stacked photomicrographic composites of 17 individual focal planes using the software package HeliconFocus version 6.3.3 Pro. Systematic paleobotany Order Porellales Schljakov, 1972 Suborder Jubulineae Müll.Frib., 1909 Family Lejeuneaceae Rostovzev, 1913 Genus Lejeunea Lib., 1820 Lejeunea aristovii Schäf.-Verw., Mamontov, K.Feldberg & Perkovsky sp. nov. (Fig. 1, 2) Type material: Holotype. SIZK-Be-18c, Rovno amber, late Eocene (Schmalhausen Institute of Zoology in Kiev). Syninclusions: Leptoscyphus davidii, Nipponolejeunea solodovnikovii, Odontoschisma dimorpha (see below), Plagiochila sp., and Radula oblongifolia. Diagnosis: The Lejeunea gametophyte is characterized by elliptic-ovate, apiculate to obtuse or narrowly rounded leaf lobes, reduced to absent leaf-lobules, and bilobed underleaves, and differs from the Paleogene Cheilolejeunea latiloba by the less falcate and longly inserted leaf lobes, reduced or absent leaf lobules, and underleaves that are longer than wide and widest in their upper third. Description: Shoot yellow-brownish, 1.5 mm long and 0.36–0.48 mm wide, creeping, unbranched. Rhizoids not observed. Stem straight, colourless, up to 64–68 μm in diameter (where observable). Epidermis of ventral merophytes at least 3 cells wide, cells with equally somewhat thickened walls, rounded-rectangular, (17.3–)18–32(–49) µm long × (9.8–)10.2–13.5 μm wide, from 1.64–1.92 to 3.3–3.8× as long as wide. Cells of dorsal stem cortex with equally somewhat thickened walls, ± rectangular, 13–21 µm long × 8–11 μm wide, ca 1.6–2.5× as long as wide. Leaves with a very long, J-shaped insertion, insertion line ca. (0.61–)0.66–0.85 of leaf width, incubous, usually planodistichous, remote to loosely imbricate, dorsally almost not interlocking, not reaching beyond the farther edge of stem. Lobe diverging at an angle of 40–80° to stem, usually almost flat, sometimes slightly elevated, slightly convex dorsally, shape widely to narrowly ovate or almost oblong, 181–255 μm long × 100–214 μm wide, ca 1.07–1.81× as long as wide, free margin entire. Dorsal margin semilunate to strongly arcuate in basal half, not ampliate at base. Apex sometimes decurved, ± rounded or obtuse or apiculate with a single acute protruding cell. Free ventral margin in proximal half straight to slightly incurved, near the end of the keel-like part gradually curved, not forming a part of the ventral lobule opening, in distal half slightly to strongly incurved. Cells in upper middle ± isodiametric, hexagonal, 13–26 μm long × 12–21 μm wide, ca 1.04–1.25× as long as wide, in lower middle 14–25 μm long × 12–19 μm wide, with brownish slightly thickened walls and distinct trigones. Ocelli absent. Keellike part (where present) 0.24–0.45(–0.55) length of lobe, smooth, convex to almost straight, with gradual transition into free margin of lobe. Lobule (if present) not available for observation. Underleaves with shallowly arcuate insertion, remote, the only available evident underleaf (Figs. 2E, 2G) flat, 167 μm long × 145 μm wide, ca. 2.5× wider than the stem, obovate, widest in its upper third, ± cuneate at base, bilobed to 0.39–0.43× the length, sinus acutangular with U-shaped base, lobes slightly converging, triangular, ca. 4 cells long, ca. 4–5 cells wide at base, moderately acute, formed by a single rounded cell, subterminally with 2 cells side by side, lateral margin in the upper half unidentate because of a protuberant cell, in the lower half somewhat sinuous. Asexual reproduction, gynoecia, and androecia not observed. Etymology: The species is named in honor of Dr. Daniil Sergeevich Aristov, an eminent paleoentomologist. Comparison: Lejeunea aristovii differs from Cheilolejeunea latiloba by its yellow-brownish colour (red-brown in C. latiloba), less falcate leaf lobes, much less prominent and frequently reduced leaf lobules, and an apiculate leaf apex with a single acute cell (if apiculate in C. latiloba, then with a single protruding rounded cell). It is therefore obvious that L. aristovii cannot be identical with C. MAMONTOV ET AL. Ecologica Montenegrina, 80, 2024, 230-243 233 Figure 1. Lejeunea aristovii (photo and line drawing): A, E – habit, dorsal aspect (parts of the same shoot). B – same, the graphic reconstruction. C – an enlarged underleaf, close-up of the area selected in Fig. 2E. D – same, the graphic reconstruction. All from SIZK-Be-18c. latiloba. Lejeunea aristovii is a very small species, but possibly only a less developed branch is at hand. The ovate to almost oblong and often apiculate leaf lobes with partly (or completely?) reduced lobules in combination with the remote and distinctly bilobed (to ca. 0.4), obovate (to ovate) underleaves seem to be very characteristic. It is possible that the majority of leaf lobes were apiculate, but the apiculus might be hidden because it is incurved and therefore not (well) visible, especially when the plant is enclosed in amber and cannot be examined like an extant species. Other fossil species of Cheilolejeunea can be easily excluded either by undivided underleaves (C. antiqua W.Ye & R.L.Zhu and C. suzannensis (Grolle) Grolle & R.L.Zhu, both from Dominican amber) or by rather different shapes of leaf lobes and HEPATICS FROM ROVNO AMBER. PART 14 234 underleaves (C. lamyi (Casp.) Grolle, also from Dominican amber). Fossil Lejeunea species are only known from the Miocene Dominican and Mexican amber. Dominican amber includes the species L. hamatiloba G.E.Lee, Schäf.-Verw., M.A.M.Renner & Heinrichs, L. miocenica Heinrichs, Schäf.-Verw., M.A.M.Renner & G.E.Lee, L. resinata G.E. Lee, Schäf.-Verw., M.A.M.Renner & Heinrichs and L. urbanoides G.E.Lee, Schäf.-Verw., M.A.M.Renner & Heinrichs (Lee et al. 2017). Recently, a small specimen of Lejeunea sp. was discovered in Mexican amber (Feldberg et al. in press). None of these species are similar to L. aristovii. Figure 2. Lejeunea aristovii (photo): A, F, J – habit, dorsal aspect (three parts of the same shoot). B, E, H – parts of the shoot, lateral aspect. C – close-up of the area selected in Fig. 2B. D – close-up of the area selected in Fig. 2F. G – close-up of the area selected in Fig. 2E. I – close-up of the area selected in Fig. 2H. All from SIZK-Be18c. MAMONTOV ET AL. Ecologica Montenegrina, 80, 2024, 230-243 235 There are some small extant species of Lejeunea and Cheilolejeunea with which L. aristovii may be compared. Lejeunea apiculata Sande Lac. is easily distinguished by a much more prominent apiculus, while L. cocoes Mitt. and L. malaysiana G.E.Lee & Pócs differ by their narrowly rounded to sometimes obtuse leaf lobe apex. Moreover, these Lejeunea species all have shorter leaf lobe insertion lines, ca. 0.38–0.67 of leaf width (according to our measures of the leaves imaged in Lee 2013). One of the smallest Lejeunea species in Asia, L. exilis (Reinw., Blume & Nees) Grolle, has distant, ovatelanceolate leaf lobes with a leaf lobe insertion line ca. 0.44–0.74 of leaf width, with mostly welldeveloped leaf lobules, and small, deeply divided or undivided lanceolate underleaves, which are not or only slightly wider than the stem. Another small species, L. tuberculosa Steph., has ovate-orbicular, broadly rounded leaf lobes without apiculus, a leaf lobe insertion line ca. 0.44–0.74 of leaf width, rarely reduced leaf lobules and underleaves that are mainly as long as wide. In fact, all other extant Lejeunea species known to us are clearly different from L. aristovii. There are no small-sized extant Cheilolejeunea species with ovate-oblong leaf lobes and an apiculate leaf apex combined with underleaves as in Lejeunea aristovii (not even among the Neotropical Cheilolejeunea species). Cheilolejeunea subopaca (Mitt.) Mizut. differs from L. aristovii by its ovatetriangular, acute leaf lobes and small underleaves, which are entire-margined and nearly orbicular, as long as wide or wider than long. Other small or tiny species have either almost orbicular, broadly rounded leaf lobes like C. intertexta (Lindenb.) Steph. or ovate to ovate-triangular leaf lobes with obtuse or acute apices like C. osumiensis (S.Hatt.) Mizut. or C. obtusifolia (Steph.) S.Hatt. Order Jungermanniales H.Klinggr., 1858 Suborder Cephaloziineae Schljakov, 1972 Family Cephaloziaceae Mig., 1904 Genus Odontoschisma (Dumort.) Dumort., 1835 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-18d, SIZK-Be-18e, SIZK-Be-18f (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 ovateoblong 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 HEPATICS FROM ROVNO AMBER. PART 14 236 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. 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-Be18e; C, G from SIZK-Be-18f. MAMONTOV ET AL. Ecologica Montenegrina, 80, 2024, 230-243 237 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-Be18f; D, E from GZG.BST.22048. 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 HEPATICS FROM ROVNO AMBER. PART 14 238 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. General discussion With the new records provided in this paper, the Rovno amber liverwort flora includes 19 species, namely Acrolejeunea ucrainica Mamontov, Heinrichs & Schäf.-Verw., Anastrophyllum rovnoi Mamontov, Heinrichs & Váňa, Cephaloziella nadezhdae Mamontov, Heinrichs & Váňa, Frullania ekaterinae Mamontov, Ignatov & Perkovsky, F. pycnoclada Grolle, F. riclefgrollei Mamontov, Heinrichs, Schäf.-Verw., Ignatov & Perkovsky, F. rovnoi Mamontov, Hentschel, Konstant., Perkovsky & Ignatov, F. schmalhausenii Mamontov, Ignatov & Perkovsky, F. vanae Mamontov, J.J.Atwood, Perkovsky & Ignatov, F. varians Casp., F. zerovii Mamontov, Ignatov & Perkovsky, Jubula polessica Mamontov, J.J.Atwood & Perkovsky, Lejeunea aristovii, Leptoscyphus davidii, Nipponolejeunea rovnoi Mamontov, Schäf.-Verw. & Perkovsky, N. solodovnikovii, Odontoschisma dimorpha, Radula oblongifolia, and R. tikhomirovae Mamontov & Perkovsky (Feldberg et al. 2021; Mamontov et al. 2024a, 2024b, 2024c, 2024d). All genera that are found in Rovno amber are commonly epiphytic, and many have been preserved in Baltic and Bitterfeld amber together, so we have another small excerpt of an epiphyte community in the studied amber piece. Until now, only three of the liverwort species discovered in Rovno amber, namely Frullania pycnoclada, F. varians and Radula oblongifolia are also known from Baltic and/or Bitterfeld amber (Grolle & Meister 2004). The record of Odontoschisma dimorpha in Rovno amber brings the floras closer together, but the other 15 species endemic to Rovno amber suggest that environmental conditions were different between the Baltic and Rovno amber forests. The close phylogenetic relationship of O. dimorpha to the pantropical section Iwatsukia of the genus Odontoschisma hypothesized in Feldberg et al. (2017) together with the previous record of Leptoscyphus davidii suggest a warmer climate in the area of the Rovno amber forests. Many arthropod records also point to at least frost-free winters on the Volhynian Uplift (e.g., Baranov et al. 2016; Matalin et al. 2021; Yamamoto et al. 2022; Telnov et al. 2021, 2023; Anisyutkin & Perkovsky 2023; Belokobylskij et al. 2023; Legalov et al. 2023a, 2023b; Loktionov et al. 2023; Lyubarsky et al. 2023; Nabozhenko & Perkovsky 2023; Turbanov et al. 2024; Jenkins Shaw et al. 2024; Perkovsky et al. 2024; Sokolov et al. 2024; Chemyreva et al. 2024b). The shoot of Lejeunea aristovii is partly attached to a defoliated stem of the Plagiochila species preserved in the same amber piece, and it is typical for Lejeunea to grow on larger liverworts in the subtropics and tropics. Despite the fact that the majority of the Lejeunea species are restricted to the tropics, the record of L. aristovii, however, cannot provide additional information to support the assumptions about the climatic conditions in the discussed area this time. The phylogenetic relationships of L. aristovii can