Jubula polessica Mamontov, J.J.Atwood & Perkovsky, 2024

Mamontov, Yuriy S., Atwood, John J., Ignatov, Michael S., Vasilenko, Dmitry V., Legalov, Andrei A. & Perkovsky, Evgeny E., 2024, Hepatics from Rovno amber (Ukraine). 12. Jubula polessica sp. nov., Ecologica Montenegrina 73, pp. 1-10 : 3-10

Jubula polessica Mamontov, J.J.Atwood & Perkovsky , sp. n. ( Fig. 1 )

Diagnosis. An incubously foliated liverwort, differs from all Frullania species by the insertion of its underleaves and the number of its floral series of bracts, from all Jubula species in the much smaller plant size, and from the morphologically similar Pseudofrullania hamatosetacea (Grolle) Heinrichs, Feldberg, M. A.M.Renner & Schäf.-Verw. and Neohattoria herzogii (S.Hatt.) Kamim. by the comparatively larger underleaves, absence of long cilia and short dense teeth on the leaf lobe apices.

Description. Plant fertile, perhaps brownish; shoot about 1.1 mm long, up to 0.57 mm wide, with no branches. Stem ca. 87–110 µm in diameter, cortical cells 15–18 µm long, 14–17 µm wide. Rhizoids not observed. Leaf lobes (badly recognizable) widely spreading, obliquely inserted, in ventral aspect plane or convex, elliptic-ovate, ca. 220–270 µm long, up to 115 µm wide, at apex bidentate to short bifid (up to 0.1 of the length), dorsal and ventral margins rounded, entire. Leaf lobe cells ca. 16– 21 × 13–17 µm, with thickened walls, lacking trigones and intermediate thickenings. Ocelli not observed. Cuticle smooth. Leaf lobules inflated, galeate, adnate with the lobe at a distance of 25–47µm from them stem, almost parallel to or slightly angled (at an angle about 20–36°) away from the stem, 127–161 µm long, 77–109 µm wide, about 1.44–1.74× as long as wide, almost symmetric or slightly asymmetric, with the anterior side ( Fig. 1B , arrows ‘A’) convex in upper quarter or in upper third and below straight, with the posterior side ( Fig. 1B , arrows ‘P’) convex in upper quarter and below straight or concave, with a broadly rounded apex, widest in upper third or in upper quarter, gradually applanate towards the mouth, not constricted above it; mouth valves (badly recognizable) entire, subparallel, equal in size, somewhat arcuate, with the length of mouth margins of ca. 0.33–0.43 of the lobule height; rostral portion of the lobule not beaked or bears an indistinct angulation ( Fig. 1B , arrows ‘B’). Styli not recognizable (if any). Underleaves 1 per leaf pair, 219–266 µm long, 112–153 µm wide, ca. 1.71–1.82× as long as wide, ca.1.1–1.75× wider than stem, long sub- lyriform, nearly transversely inserted, but somewhat inclined on one side, distant to contiguous, gradually broadened in the middle from a cuneate base, widest in lower third or near middle; concave in the lower third, flat to little convex in the middle, with no distinct rhizoidal area; margins plane; bifid to 0.47–0.62 of the length, sinus narrowly U-shaped, the sinus base rounded; lobes erect, longly acute to acuminate-ciliate, otherwise entire, narrowly triangular, mostly directed towards the stem apex, ca 2.4–2.9× as long as wide, inner margins of lobes entire, slightly to distinctly arcuate, basal portions of inner margins, and sometimes sinus, ± reflexed; underleaves inserted on an arcuate line, the cuneately narrowed bases decurrent. Asexual reproduction not observed. Gynoecia terminal (a single one known), one subfloral innovation of (possibly) Radula - type present. Gynoecial bracts ( Fig. 1A, C ) in a single series (according to the number of the tips of lobes and lobules), enlarged, their lobes lanceolate, ca. 330–350 µm, 120–130 µm wide, ca 2.7–2.8× as long as wide, apex apiculate, the margins otherwise entire; the bract lobules and the lobes of bracteole ending with lanceolate-ciliate tips; other details unresolved in the available specimen.

Etymology. The species is named after its locus classicus situated in Ukrainian Polissya, part of the Polesian Lowland.

Type material. Holotype. SIZK-Be-18b, Belokorovichi, Rovno amber. Syninclusions: Leptoscyphus davidii ( Mamontov et al. 2024a), Nipponolejeunea sp. , and Radula oblongifolia Casp. ( Mamontov et al. 2024b) .

Comparison. Among the leafy liverworts known from the Eocene, Jubula polessica is most similar to Pseudofrullania hamatosetacea and two Frullania species described from Baltic and Bitterfeld amber ( F. baltica Grolle ) and from Rovno amber ( F. schmalhausenii Mamontov, Ignatov & Perkovsky ) in the shape and arrangement of its leaf lobules. In fact, all of these species, alongside with J. polessica , have leaf lobules that are tilted outwards at 20° to 75°, are clavate in outline, distinctly longer than wide, not constricted and not or slightly applanate near the mouth, have equal mouth margins, with the mouth apex (the point of mouth valves junction) at the height of less than 0.1 of the lobule height, and have the base of the lobule adnate with the lobe at about 28–90 μm from the stem. However, J. polessica differs from all of these species in its relatively larger underleaves that are ca. 1.7–1.8× as long as the lobules. By comparison, the underleaves of P. hamatosetacea , F. baltica and F. schmalhausenii are only 0.7–1.6× as long as the lobules. Pseudofrullania hamatosetacea also differs from the new species by the presence of long uniseriate awns at the leaf lobe apex, whereas F. baltica and F. schmalhausenii differ in their underleaf shape, which is obovate to rhomboidal, not or slightly longer than wide, widest in upper half, and bilobed with rather wide triangular lobes. The underleaves in J. polessica are 1.71–1.82× as long as wide, long sub-lyriform, and are widest in the lower third or near the middle.

Discussion

Among the extant leafy liverworts, in the order Porellales , only members of the families Frullaniaceae and Jubulaceae have comparable vegetative morphology that is consistent with J. polessica . That is, the underleaves are bifid (but not quadripartite) and lack watersacs, in contrast to the otherwise superficially similar Lepidolaenaceae that has underleaves often with a pair of ciliately toothed watersacs. The last taxonomic treatment of all groups of species having this type of morphology recognized six genera within the Jubulaceae , namely Amphijubula R.M.Schust. , Frullania , Jubula , Neohattoria , Schusterella S.Hatt. & Mizut. , and Steerea S.Hatt. & Kamim. ( Schuster 1992: 10, 11). However, Crandall-Stotler et al. (2009) in a phylogenetic classification scheme that integrated morphological data with molecular hypotheses, found the Frullaniaceae and Jubulaceae to be separate families within the suborder Jubulineae . In this classification the genera Amphijubula , Neohattoria , Schusterella , and Steerea are considered to be synonymous with Frullania . A later molecular phylogenetic study of the Jubulineae by Larraín et al. (2015), however, demonstrated Frullania herzogii S.Hatt. (≡ Neohattoria herzogii ) to have a sister position within the Jubulaceae with Nipponolejeunea S.Hatt. , thus reinstating the genus Neohattoria .

The joining of Amphijubula , Schusterella and Steerea within Frullania enabled a rather straightforward assignment of extant species having the relevant morphology to one of the two lineages – Frullaniaceae or Jubulaceae – based on the distinctions listed in Larraín et al. (2015). These include: (1) the presence of reddish secondary pigmentation in Frullania vs. soft plants without secondary pigmentation (thus colors only up to pale brown) in the Jubulaceae , and (2) the shape of the initial branch leaves (bifid or trifid vs. triangular and never tri- or bifid, respectively). However, in the case of fossil liverworts, these distinctions sometimes cannot be implemented since the evaluation of the color (reddish vs. brownish) of amber inclusions can be subjective. Moreover, reddish pigmentation is sometimes absent in isolated shoots or even whole mats of different extant Frullania species, such as in F. acutiloba Mitt. , F. ericoides (Nees) Mont. and F. stipatiloba Steph. Furthermore , the initial branch leaves of the shoots that are embedded in amber pieces are difficult if not impossible to study due to the scarcity of material or the presence of organic residues that cover up parts of the shoots and block critical details of the branches. The attributing of the majority of Frullania -like Eocene fossils to the genus Frullania rather than to the Jubulaceae is, nevertheless not of serious concern due to the similarity of these fossils to extant Frullania species, particularly in the shape of their leaf lobes, lobules and underleaves, as well as in the comparatively firm structure of the shoots (in contrast to the more softtextured plants of Jubulaceae species). An exception, however, are two fossil species that are different from Frullania but similar to the Jubulaceae in isolated morphological characteristics, and where the shape of the initial branch leaves is not available for observation. One of these species is Pseudofrullania hamatosetacea (≡ Frullania hamatosetacea Grolle ) described from Bitterfeld amber ( Grolle & Meister 2004: 22–23); the other is the newly described Jubula polessica .

In the original description of F. hamatosetacea, Grolle & Meister (2004) compared the morphological similarities between this species and the extant F. herzogii S.Hatt. (≡ Neohattoria herzogii ) and Nipponolejeunea subalpina (Horik.) S.Hatt. This included the presence of long awns at the tips of the leaf lobes (a superficial resemblance to N. subalpina ) and the presence of saccate-clavate watersacs, dentate margin of the leaf lobe, shape of the underleaves, and small size of the plants (morphologically resembling F. herzogii ). Based upon the close similarities between F. hamatosetacea and F. herzogii, Grolle & Meister (2004) placed the former species into the same subgenus as F. herzogii (F. subg. Dentatiloba Stotler & Crand.-Stotl.). Heinrichs et al. (2018) transferred F. hamatosetacea into a separate extinct genus, Pseudofrullania , and distinguished it from Neohattoria herzogii by its (1) leaf lobe insertion, (2) the presence of incurved ciliate teeth along the leaf margin, (3) a reddish-brown color, and (4) the lack of caducous leaves. The systematic position of this genus remains unresolved between the Frullaniaceae and Lepidolaenaceae , although Heinrichs et al. (2018) note that the leaf lobules in Pseudofrullania hamatosetacea are eciliate, and that the underleaves do not bear watersacs, characteristics of the branch underleaves in extant and fossil Lepidolaenaceae ( Grolle 1967; Heinrichs et al. 2014 b). Grolle & Meister (2004) characterized F. hamatosetacea as red-brown in color, and Heinrichs et al. (2018) also note this color among the distinctions between this species and N. herzogii . However, Grolle & Meister (2004) similarly described the same red-brown color also for Eocene plants of Cheilolejeunea latiloba (Casp.) Grolle , Metacalypogeia baltica Grolle , and N. subalpina , whereas the extant species of the genera Cheilolejeunea (Spruce) Steph. , Metacalypogeia (S.Hatt.) Inoue , and Nipponolejeunea are devoid of reddish secondary pigment, but can sometimes be yellow or brownish in color ( Mizutani 1961; Schuster 1969, 1980). The “red- brown” color description given in Grolle & Meister (2004), therefore, may be merely an indication of the color that the studied shoots manifest in amber (possibly in relation to the depth of embedment and the light source used to study them), and are not an indication of the intravital presence of reddish secondary pigmentation in these Eocene species. If this is indeed the case, then of the discussed features, only the not or weakly ampliate leaves with ciliate teeth along the margin distinguishes P. hamatosetacea from Frullania . As noted in Heinrichs et al. (2018), such leaves occur in the Lepidolaenaceae , rather than the Frullaniaceae , although similar, weakly ampliate leaf lobes also occur in some phases of J. blepharophylla Grolle ( Guerke 1978: 93, Fig. 11), J. hutchinsiae (Hook.) Dumort. subsp. hutchinsiae ( Guerke 1978: 94, Fig. 15) and N. subalpina (the Jubulaceae ). Furthermore, most species of Jubulaceae have uniseriate teeth or ciliae (similar to those of P. hamatosetacea ) on the leaf lobe margins, moreover in J. blepharophylla and Nipponolejeunea species the ciliae are sometimes nearly equal in length with the leaf lobe ( Mizutani 1961: 144, Fig. IV: 3; Guerke 1978: 93, Fig. 11). Since the underleaves of P. hamatosetacea lack watersacs – in contrast to members of the Lepidolaenaceae – this species also aligns with the Jubulaceae in all of the discussed morphological characteristics. Therefore, the genus Pseudofrullania is considered here to more likely belong to the latter family.

As for J. polessica , the combination of its morphological features places this species more closely with Jubula , Neohattoria and Pseudofrullania rather than with Frullania , Gackstroemia and Lepidogyna . In the case of species of Gackstroemia and Lepidogyna , only the ultimate branches of their pluribranched shoot systems are comparable in size with the new fossil. Furthermore, the underleaves of these ultimate branches are usually provided with watersacs on one or both sides. In addition, the line of insertion of the underleaf in J. polessica lies on the stem clearly lower in acropetal order than the point of attachment of the leaf lobules. This characteristic is in contrast to the vast majority of Frullania species where the line of insertion of the underleaf usually lies on the stem very close or parallel to, and almost coinciding with, the point of attachment of the stylus and lobule to the stem. This type of underleaf insertion, such as in J. polessica , is characteristic of the family Lejeuneaceae (see, for example, Schuster 1980: Fig. 670: 8, 9; 675: 5, 7), however the species of Jubula (see Paton 1999: 478), N. herzogii ( Kamimura 1961: Fig. XXXIII: 2, 3) and seemingly P. hamatosetacea also show a tendency to have their underleaves inserted in the same way (i.e. not very close to the base of any of the opposed leaf lobules in a leaf pair). The similar, but unusual for Frullania , position of the underleaves relative to the position of the leaf lobules is however depicted for one shoot of F. apicalis Mitt. by Vanden Bergen (1976: Fig. 12A). This character state therefore does not per se exclude attributing the placement of J. polessica within the genus Frullania , especially since such scarce material is available for study. However, the shape of the underleaves in the J. polessica is regardless to be more similar to those of Jubula (see Schuster 1992: 24, Fig. 776: 2) and Neohattoria than to Frullania . For example, there are no extant Frullania species where the underleaves are simultaneously entire margined, ±clearly decurrent, and bifid more than half of their length into long attenuate lobes. Also, the possible absence of styli in the new fossil testifies in favor of a relationship with Jubula and Neohattoria , where the stylus is similarly vestigial, unicellular or represents a mere slime papilla ( Kamimura 1961; Schuster 1992). The new fossil is also similar to the Jubulaceae (especially Jubula species) in the single floral series of the gynoecial leaves in its gynoecium, and in its subfloral innovation ( Fig. 1A, C ) that is supposedly of Radula - type. In contrast to Jubula , Frullania species have 2–5 series of the gynoecial leaves and only Frullania - type innovations are developed ( Mizutani 1961; Schuster 1992). In the shoot studied here, the view of the gynoecium and the base of the mentioned innovation are too obscure to depict critical details of their morphology, however the positions of the gynoecium, the innovation, and the uppermost (in acropetal order) sterile underleaf in the main shoot correspond to a normal merophyte of the leafy liverworts. In the vegetative parts of shoots of leafy liverworts, a merophyte usually consists of an underleaf and two opposed leaves, and in the studied shoot the gynoecium and the innovation replace their corresponding leaves and associate with the uppermost sterile underleaf likely in the same way as that is depicted for two gynoecial shoots of J. pennsylvanica (Steph.) A.Evans ( Schuster 1992: Fig. 822: 1, 2). Furthermore, in the studied shoot there is no leaf lobe that could be considered to be associated with the innovation, which challenges the possible treatment of the innovation as a Frullania - type branch. Therefore, the innovation is considered more likely to be of Radula - type.

By the combination of all these characteristics, the new fossil is best considered as a member of the Jubulaceae , however the generic placement of this species is not exactly clear and is worthy of discussion. The leaf lobules of J. polessica are 1.54–1.74 times longer than wide and are more reminiscent of those of numerous Frullania species, but also are similar to N. herzogii and P. hamatosetacea . By comparison, the leaf lobules of Jubula species usually have a smaller length/width ratio. Nevertheless, Kamimura (1961: Fig. XXXII: 1, 20), Mizutani (1961: Fig. III: 10), Chang & Gao (1984: Fig. 8: 1, 2), Grolle (1967: Abb. 3c), Srivastava & Sharma (1990: Figs. 5, 6), and Schuster (1992: Fig. 822: 2) illustrate shoots of different Jubula species having isolated leaf lobules that are elongate and quite similar in outline to those of the new fossil. The leaf lobules in J. polessica are adnate to the lobes at a remote distance from the stem with their mouths usually pointing toward the base of the shoot. By contrast, N. herzogii , has lobules that are positioned much closer to the stem with the lobule apex touching or nodding towards the stem and the mouths pointing proximally. However, the plant size of J. polessica and the ratio of the size of its leaf lobes to its leaf lobules, are much smaller than that of all Jubula species and approach that observed in N. herzogii . Moreover, in almost all extant Jubula species (except J. kwangsiensis C.Gao & K.C.Chang ) the ratio of the size of the underleaves to the size of leaf lobules is larger than in Neohattoria and the new fossil. Also, the underleaf margins of N. herzogii and the new fossil are consistently entire compared to that of extant Jubula species where the underleaf margins often have a few to many teeth. Therefore, based on plant size, the shape and proportions of the leaf lobes, and the morphology of the lobules and underleaves, the new fossil has features that are seemingly consistent with those of Neohattoria and suggest affinities with that genus. Nevertheless, we find the combination of gametophytic and gametangial characters, that is the more distant lobule position coupled with the gynoecium having a pair of bracts and a bracteole with entire margins and arranged in a single floral series, to more strongly supportive of the fossil’s placement in Jubula . Mature gynoecial leaves are yet unknown for N. herzogii . However, immature bracts and bracteoles of the species are arranged in three floral series with the bracts progressively larger and having consistently dentate margins nearly to the base ( Stotler & Crandall-Stotler 1987).

Finally, the ecology of J. polessica is similar to both that of N. herzogii [a strictly corticolous species ( Kamimura 1961; Mizutani 1961; Bakalin 2019)] and the East Asian J. kwangsiensis [also strictly corticolous ( Chang & Gao 1984)]. Interestingly, J. polessica is found together with a Nipponolejeunea species in a syninclusion within the same amber piece (SIZK-Be-18). Neohattoria herzogii frequently occurs with extant Nipponolejeunea , N. subalpina , based on collections from the middle and northern Japan ( Kamimura 1961) as well as from the Kunashir Island (these collections made by the first author and are preserved in the MHA herbarium). Although North American and European Jubula occur only in rocky habitats ( Schuster 1992; Paton 1999), the Asian J. hattorii Udar & Vir. Nath , J. himalayensis S.C.Srivast. & D. Sharma , as well as the J. hutchinsiae subsp. javanica (Steph.) Verd. distributed in East, South-East and South Asia, sometimes occur on tree trunk bases and the bark of trees besides soil and rocks ( Kamimura 1961; Mizutani 1961; Udar & Nath 1978; Srivastava & Sharma 1990), while J. blepharophylla is epiphyllous on filmy ferns ( Hymenophyllaceae ) in the forests of New Guinea ( Grolle 1965).

Together with P. hamatosetacea and the four fossil species of Nipponolejeunea ( Grolle & Meister 2004; Mamontov et al. 2024, in press), Jubula polessica brings the number of European Eocene Jubulaceae to six species. This number greatly exceeds the diversity of extant members of the family in Europe (one species) and is equal only to the diversity of Jubulaceae in East Asia. As for the regions of East Asia, the maximum number of extant Jubulaceae (four species) is found in Honshu ( Yamada & Iwatsuki 2006; Pätsch et al. 2010), where the species of this family, however, occur in rather different environments – from low mountains in the case of Jubula species to middle and high mountains in the cases of Neohattoria and Nipponolejeunea species.

Since the combination of features of J. polessica (the gynoecium having a single floral series of bracts together with the more distant lobule position and the shape (rather deeply bilobed and decurrent) and the distant insertion of underleaves) is characteristic of extant members of the genus Jubula , the finding of this species directly points to at least Eocene if not pre-Eocene origin of the stem group of Jubula . Until now, indirect indications on the possible Paleogene origin of this genus were the records of the Eocene species of the genus Nipponolejeunea coupled with the molecular phylogenies showing a sister relationship between Nipponolejeunea and Jubula (e.g. Ahonen 2004; Forrest et al. 2006; Heinrichs et al. 2005, 2007; Larraín et al. 2015). In Heinrichs et al. (2018: Fig. 12.2 and Tab. 12.2), the upper limit of the divergence time between the common ancestors of extant Jubula and Nipponolejeunea lies in the middle of the Cretaceous (104.64 Ma), while the lower limit of this time interval is in the late Oligocene (26.74 Ma), and the mean value (62.12 Ma) is near the middle of the Paleocene. The finding of J. polessica together with the records of the fossil Nipponolejeunea species point to the existence of both genera in the Eocene. Therefore, the mean value of the time of their divergence provided in Heinrichs et al. (2018) may be closer to the real age of this event in comparison with the lower limit of the estimated time interval.

Acknowledgements

The authors are very grateful to Nadezhda A. Konstantinova and Alexandr P. Rasnitsyn ( Russia), Alfons Schäfer- Verwimp ( Germany), and Juan Larraín ( Chile) for critical suggestions and valuable comments. The study by E.E. Perkovsky was supported by the Scholars at Risk Ukraine (SARU) program jointly funded by the Villum Foundation, Carlsberg Foundation and the Novo Nordisk Foundation.

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Figures

Figure 1. Jubula polessica sp. n., photo and drawing. A, C – general view of the inclusion, two parts of the same shoot, ventral aspect; B – graphic reconstruction of the shoot, ventral aspect.