Selaginella ovoidea 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 : 216-218

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

Holotype: AMNH-Bu-KL-8-7 [ Fig. 25], American Museum of Natural History. – Fig. 2G; 25 (only specimen available).

Diagnosis — Axes compressed. Trophophylls dimorphic. Dorsal trophophylls close, adpressed, symmetric, ovate, non-carinate, base decurrent, apex aristate, sparsely dentate at margins. Ventral trophophylls close, slightly imbricate, spreading, ascending, somewhat asymmetric, ovate, non-carinate, base decurrent, acute at apex, sparsely denticulate to dentate at margins. Strobilus terminal, compact, tetrastichous, quadrangular. Sporophylls monomorphic, imbricate, adpressed, conduplicate, lanceolate, carinate, base rounded, apex long-attenuate, serrulate at margins, sporophyll-pteryx absent. Sporangia ellipsoid or ovoid. Microspores in tetrads, distally rugulate.

Description — Rhizophores not preserved. Axes compressed. Trophophylls dimorphic ( Fig. 25A, H–J). Axillary trophophylls not preserved. Dorsal trophophylls close, adpressed, symmetric, 0.6–0.8 × 0.3–0.4 mm, ovate, non-carinate, base decurrent, apex aristate, margins sparsely dentate, teeth 12–35 µm long ( Fig. 25I). Ventral trophophylls close, slightly imbricate, spreading, ascending, somewhat asymmetric, 1.3–1.5 × 0.5–0.6 mm, ovate, non-carinate, base decurrent, apex acute, margins sparsely denticulate to dentate, teeth 8–40 µm long ( Fig. 25H, J). Epidermis of dorsal and ventral trophophylls composed of uniform isodiametric cells ( Fig. 25J). Strobilus terminal, compact, tetrastichous, quadrangular, 4.6 × 0.9 mm ( Fig. 25A, B). Sporophylls monomorphic, imbricate, adpressed, conduplicate, 28 in only available strobilus, 1.0–1.5 × 0.2–0.3 mm, lanceolate, carinate, base rounded, apex long-attenuate, margins serrulate, teeth <10 µm long, sporophyll-pteryx absent ( Fig. 2G; 25B). Epidermis of sporophylls poorly preserved. Sporangia ellipsoid or ovoid, 480–600 × 220–280 µm, formed by uniform isodiametric cells bearing thick anticlinal walls ( Fig. 25C, D). Microspores in tetrads, distally rugulate ( Fig. 25E–G).

Remarks — Selaginella ovoidea is the only Kachin Selaginella that is characterized by quadrangular strobili with very distinctive ellipsoid or ovoid sporangia ( Fig. 25C, D).

Among extant Selaginella , two species closely resemble the fossil, namely S. rolandi-principis Alston from China and Vietnam ( Zhang & al. 2013) and S. roxburghii (Hook. & Grev.) Spring , native to the Malay Peninsula, Vietnam ( Alston 1937) and presumably also China according to Zhang & al. (2013), who referred to this taxon using the synonym S. commutata Alderw. These species share with the fossil the presence of ovate, aristate or cuspidate dorsal trophophylls, oblong-ovate ventral trophophylls that are sparsely denticulate at the margins, quadrangular strobili with lanceolate to ovate sporophylls with an acute to attenuate apex and serrulate margins, and ellipsoid sporangia. Additionally, both S. rolandi-principis and S. ovoidea produce microspores in tetrads, although it is not possible to be sure that this is a permanent condition in either of them. Both S. rolandi-principis and S. roxburghii differ from S. ovoidea in that the microspores have a baculate ornamentation on the distal surface ( Zhou & al. 2015a), which differs from the rugulate pattern seen on the distal surface of the fossil microspores ( Fig. 25F).

Etymology — The specific epithet is derived from the Latin word ovoideus and refers to the egg-shaped sporangia.