Radula Dumort., 1822

Mamontov, Yuriy S., Ignatov, Michael S., Vasilenko, Dmitry V., Legalov, Andrei A. & Perkovsky, Evgeny E., 2024, Hepatics from Rovno amber (Ukraine). 11. Radula oblongifolia and R. tikhomirovae sp. nov., Ecologica Montenegrina 72, pp. 189-199 : 191

Genus Radula Dumort., 1822

Radula oblongifolia Casp., Schriften der Königlichen Physikalisch- Ökonomischen Gesellschaft zu Königsberg 27: 4. 1887. Fig. 1 .

Type material: Neotype: Geoscientific collections of the Georg August University Göttingen, Germany, GZG. BST. K7.323 ( Heinrichs et al. 2016: Plate II, Fig. 5.v).

Description: Pale yellowish gametophyte, the available part of shoot unbranched, ca. 2.3 mm long, up to 0.6 mm wide. Stem ca. 75–80 µm in diameter, cortical cells elongate- rectangular, 14–19 µm long, 13–16 µm wide. Leaves continuous, rather remote, the parts of the stem free from leaves are comparable with the leaf lobes in their length. Leaf lobes spreading, obliquely patent in plane, with the angle between stem axis and the long axis of a lobe (from the middle of lobe apex to the middle of lobe insertion) is about 44–75°, elliptic, the length 232–367 μm, the overall width 208–314 μm, postical margin straight to curved, always short, exterior margin rounded, antical margin weakly curved, interior margin weakly ampliate, usually extending onto the dorsal stem surface, but leaving the stem visible from above. Leaf lobules extend to ca. 0.4–0.6 times the area of the leaf lobes; elliptic to rhomboidal, the lobule breadth 152–265 μm, the lobule depth 157–202 μm, insertion longitudinal; keel straight, arising from stem at 44–75° angle; exterior and antical margins straight to slightly curved, apex obtuse; interior margin likely not ampliate, not extending onto ventral surface of the stem. Strip-shaped dorsal leaf-free zone present, one cortical cell row wide; presence or absence of the ventral leaf-free strip not ascertained. Cells on leaf lobe margin quadrate to rectangular, 15–23 μm long, 13–20 μm wide, long axis either perpendicular to, or parallel with, the lobe margin; medial cells rectangular to hexagonal, 20– 24 μm long, 14–20 μm wide, basal cells similar to mid- leaf cells, sometimes larger; cell wall thickenings not resolved. Asexual reproduction not observed. Gynoecia, androecia, and sporophytes not observed.

Specimen examined: Rovno amber: SIZK-Be-18c ( Schmalhausen Institute of Zoology in Kiev).

Comparison: As stressed above, the studied plant can be considered to be poorly developed (perhaps etiolated) because it is rather small-sized (with the shoot width up to 0.62 mm) and rather remotely foliated, with obliquely oriented leaves. By contrast, the neotype plants of R. oblongifolia are up to 1.43 mm wide and are more densely foliated, with overlapping leaf lobes. In the studied shoot, the proportions between the overall width of the leaf lobe and the breadth of the leaf lobule are similar to those of R. oblongifolia . However, the leaf keel in the Rovno plant is relatively shorter, giving the leaf lobules a somewhat different in shape from the majority of leaf lobules of the latter species. Indeed, in the Rovno plant the leaf lobules are elliptic to rhomboidal, whereas in the Baltic plants of R. oblongifolia they are quadratic to rectangular. However, the less-developed leaves in the Baltic plant of R. oblongifolia ( Heinrichs et al. 2016: Plate II, Fig. 1 ) have lobules that are similar to those of the studied here plant. Because no other differences from the Baltic plants of R. oblongifolia have been found, the plant studied here is considered more likely belong to this species.

Figures

Figure 1. Radula oblongifolia (SIZK-Be-18c, photo and drawing): A – habit, dorsal aspect, B – same, C – leaf lobe cells.