Selaginella aurita 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 : 210

Selaginella aurita A. R. Schmidt & L. Regalado , sp. nov. Holotype: GZG.BST.22001 [ Fig. 20], Geoscientific Collection of the University of Göttingen. – Fig. 2C; 20, 21 (two specimens available).

Diagnosis — Axes compressed. Trophophylls dimorphic. Dorsal trophophylls distant, adpressed, lanceolate, non-carinate, apex long-aristate, margins entire. Ventral trophophylls distant, ascending, symmetric, oblong-lanceolate, apex acute, base short-truncate, margins nearly entire or sparsely denticulate, non-carinate. Strobilus terminal, compact, tetrastichous, quadrangular. Sporophylls monomorphic, imbricate, somewhat conduplicate, lanceolate, carinate, base auriculate on acroscopic side, apex acute, margins sharply dentate; sporophyll-pteryx nearly complete, auriculate at base, with dentate margins similar to sporophyll margins. Sporangia suborbicular. Microspores proximally rugulate.

Description — Rhizophores not preserved. Axes compressed. Trophophylls dimorphic ( Fig. 20A, F; 21). Axillary trophophylls not preserved. Dorsal trophophylls distant, adpressed, 1.0–1.6 × 0.2–0.6 mm, lanceolate, non-carinate, base not seen, apex long-aristate, margins entire ( Fig. 21C, D). Ventral trophophylls distant, ascending, symmetric, 1.5–1.8 × 0.4–0.7 mm, oblong-lanceolate, non-carinate, base short-truncate, apex acute, margins nearly entire or sparsely denticulate ( Fig. 20F; 21B). Epidermis of dorsal and ventral trophophylls poorly preserved. Strobilus terminal, compact, tetrastichous, quadrangular, 7.5 × 3.5 mm ( Fig. 20A, B). Sporophylls monomorphic, imbricate, somewhat conduplicate, c. 72 in only available strobilus, 1.5–1.9 × 0.5–0.9 mm, lanceolate, carinate, base auriculate on acroscopic side, apex acute, margins sharply dentate, teeth 5–35 µm long ( Fig. 2C; 20C–E); sporophyll-pteryx nearly complete, auriculate at base, with dentate margins similar to sporophyll margins ( Fig. 2C; 20C–E). Sporophyll epidermis poorly preserved. Sporangia suborbicular, 500–740 × 400–560 µm, composed of uniform isodiametric cells with very thick anticlinal walls ( Fig. 20G). Microspores 20–30 µm in diam., proximally rugulate ( Fig. 20H, I).

Remarks — Selaginella aurita differs from all other Kachin Selaginella fossils by its monomorphic sporophylls, which are acroscopically auriculate ( Fig. 2C; 20C–E). Furthermore, S. aurita is the only form with quadrangular strobili bearing a sporophyll-pteryx on monomorphic sporophylls ( Fig. 2C; 20C–E). This structure is present in all four rows of sporophylls. In our comparisons to extant species from Asia, Australasia and Africa, we could not find any morphology that is particularly close to that seen in this fossil-species.

Etymology — The specific epithet is derived from the Latin word auritus: eared, auriculate, and refers to the acroscopic base of the sporophyll and to the sporophyll-pteryx.

Additional specimens studied — PB25336, Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences ( Fig. 21).