Selaginella pellucida A. R. Schmidt & L. Regalado, 2022

Schmidt, Alexander R., Korall, Petra, Krings, Michael, Weststrand, Stina, Bergschneider, Lena, Sadowski, Eva-Maria, Bechteler, Julia, Rikkinen, Jouko & Regalado, Ledis, 2022, Selaginella in Cretaceous amber from Myanmar, Willdenowia 52 (2), pp. 179-245 : 223-225

Selaginella pellucida A. R. Schmidt & L. Regalado , sp. nov.

Holotype: GZG. BST.22027 [ Fig. 30], Geoscientific Collection of the University of Göttingen. – Fig. 2J; 30 (only specimen available).

Diagnosis — Axes compressed. Trophophylls dimorphic. Axillary trophophylls asymmetric, narrowly elliptic, non-carinate, base obtuse to rounded, apex acute to slightly acuminate, margins serrate-dentate. Dorsal trophophylls distant, adpressed, conduplicate, ovate, carinate, base obtuse and decurrent, apex aristate, dentate at margins. Ventral trophophylls slightly asymmetric, distant, spreading, ascending, elliptic, non-carinate, base rounded to obtuse, somewhat decurrent, apex acute to slightly acuminate, basiscopic margin denticulate, acroscopic margin dentate. Strobili terminal, tetrastichous, quadrangular. Sporophylls monomorphic, imbricate, ascending, conduplicate, ovate, carinate, carina slightly erose, base rounded, apex attenuate, margins somewhat denticulate to erose, sporophyll-pteryx absent. Sporangia mostly suborbicular, sometimes ellipsoid. Microspores in tetrads, distally rugulate.

Description — Axes compressed. Trophophylls dimorphic ( Fig. 30B–D). Axillary trophophylls asymmetric, 0.8–1.4 × 0.3–0.7 mm, narrowly elliptic, non-carinate, base obtuse to rounded, apex acute to slightly acuminate, margins serrate-dentate, teeth 20–40 µm long. Dorsal trophophylls distant, adpressed, conduplicate, 0.8–1.0 × 0.3–0.4 mm, ovate, carinate, base obtuse and decurrent, apex aristate, margins dentate, teeth 30–60 µm long ( Fig. 30D). Ventral trophophylls slightly asymmetric, distant, spreading, ascending, 1.1–2.7 × 0.5–0.8 mm, elliptic, non-carinate, base rounded to obtuse, somewhat decurrent, apex acute to slightly acuminate, basiscopic margin denticulate, teeth ≤ 10 µm long, acroscopic margin dentate, teeth 15–60 µm long ( Fig. 30D). Epidermis of dorsal and ventral trophophylls composed of uniform isodiametric cells ( Fig. 30D). Strobili terminal, tetrastichous, quadrangular, 1.2–1.6 × 0.7–0.8 mm ( Fig. 30C). Sporophylls monomorphic, imbricate, ascending, conduplicate, c. 12 per strobilus, 0.9–1.0 × 0.3–0.4 mm, ovate, carinate, carina slightly erose, base rounded, apex attenuate, margins slightly denticulate to erose, teeth ≤ 10 µm long, sporophyll-pteryx absent ( Fig. 2J). Epidermis of sporophylls poorly preserved. Sporangia mostly suborbicular ( Fig. 30C), sometimes ellipsoid, 300–350 × 220–300 µm, with uniform isodiametric cells with thick anticlinal walls. Microspores in tetrads, distally rugulate ( Fig. 30E).

Remarks — Selaginella pellucida differs from the morphologically similar S. wangboi , S. tomescui and S. obscura by having sporophylls with somewhat denticulate to erose margins, with teeth ≤ 10 µm long and a slightly erose carina ( Fig. 2J). Conversely, the aforementioned species possess sporophylls with dentate or serrate margins, with teeth 10–40 µm long and a serrate or denticulate carina.

This fossil-taxon is morphologically similar to several extant species, including Selaginella brachyblepharis , S. involvens , S. moellendorffii and S. radicata . However, it differs from all of them by its shorter strobili (up to 1.6 mm long) and in having microspores with a rugulate distal surface (see remarks under S. wangboi for further discussion).

Etymology — The specific epithet is derived from the Latin word pellucidus, which refers to the semi-translucent, delicate preservation of the tissue in this fossil.