Selaginella heinrichsii 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 : 212-213

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

Holotype: GZG. BST.22004 [ Fig. 23], Geoscientific Collection of the University of Göttingen. – Fig. 2E; 23 (only specimen available).

Diagnosis — Axes compressed. Trophophylls dimorphic. Axillary trophophylls symmetric, broadly ovate, non-carinate, base rounded to obtuse, apex acute, margins nearly entire or serrulate. Dorsal trophophylls distant, adpressed, ovate, non-carinate, base slightly decurrent, apex obtuse, margins serrate-serrulate. Ventral trophophylls mostly symmetric, occasionally asymmetric, distant, spreading, ascending, oblong-ovate, non-carinate, base with basiscopic side rounded and acroscopic side truncate, apex obtuse to acute, margins serrate-serrulate. Strobili terminal, tetrastichous, quadrangular. Sporophylls monomorphic, distant, spreading, ascending, conduplicate, ovate, carinate, base exauriculate, apex attenuate, margins profusely denticulate, sporophyll-pteryx absent. Sporangia suborbicular, a single considerably larger sporangium situated at base of strobilus. Microspores proximally psilate.

Description — Rhizophores not preserved. Axes compressed. Trophophylls dimorphic ( Fig. 23A, H). Axillary trophophylls symmetric, c. 1.4 × 0.8 mm, broadly ovate, non-carinate, base rounded to obtuse, apex acute, margins nearly entire or serrulate, teeth ≤ 10 µm long ( Fig. 23H). Dorsal trophophylls distant, adpressed, 1.2–1.7 × 0.5–0.9 mm, ovate, non-carinate, base slightly decurrent, apex obtuse, margins serrate-serrulate, teeth 8–30 µm long ( Fig. 23H). Ventral trophophylls mostly symmetric, occasionally asymmetric, distant, spreading, ascending, 1.2–2.3 × 0.9–1.2 mm, oblong-ovate, non-carinate, base with basiscopic side rounded and acroscopic side truncate, apex obtuse to acute, margins serrate-serrulate, teeth 10–30 µm long. Epidermis of dorsal and ventral trophophylls composed of rectangular cells ( Fig. 23I). Strobili terminal, tetrastichous, quadrangular, c. 6.0 × 1.8–2.3 mm ( Fig. 23A, C). Sporophylls monomorphic, distant, spreading, ascending, conduplicate, c. 56 per strobilus, 0.7–1.2 × 0.5–0.7 mm, largest basal one 1.7–2 × 1.4–1.5 mm, ovate, carinate, base exauriculate, apex attenuate, margins profusely denticulate, teeth 10–25 µm long, sporophyll-pteryx absent ( Fig. 2E; 23C–E, G). Epidermis of sporophylls composed of elongate cells, with long axes orientated uniformly parallel to carina. Sporangia suborbicular, 280–400 × 450–550 µm ( Fig. 23F), a single considerably larger sporangium situated at base of strobilus 0.8–1.1 × c. 1.5 mm ( Fig. 23G), with uniform isodiametric cells with thick anticlinal walls. Microspores 25–30 µm in diam., proximally psilate ( Fig. 23B).

Remarks — Selaginella heinrichsii clearly differs from the other fossil Selaginella with dimorphic trophophylls, quadrangular strobili and monomorphic sporophylls in possessing dorsal trophophylls that are apically obtuse and distant sporophylls that are exauriculate at the base ( Fig. 2E; 23C–E, G, H).

Two extant species from SE Asia share the gross morphology with Selaginella heinrichsii by having oblong, apically obtuse ventral trophophylls, which are denticulate or serrulate at the margins, and quadrangular strobili with monomorphic, ovate sporophylls, the latter acute, apically attenuate or acuminate, abaxially carinate and denticulate at the margins. These species include S. brooksii Hieron. from Borneo and S. lonkobatu Hieron. & Alderw. from Maluku and Sulawesi ( Van Alderwerelt van Rosenburgh 1915). However, both differ from the fossil by having strobili with imbricate sporophylls that are rounded at the base ( Van Alderwerelt van Rosenburgh 1915), whereas S. heinrichsii has lax strobili with distant sporophylls that are exauriculate at the base ( Fig. 2E; 23C–E, G). Additionally, S. lonkobatu has dorsal trophophylls that are gradually cuspidate at the apex ( Van Alderwerelt van Rosenburgh 1915) in contrast to the obtuse dorsal trophophylls seen in the fossil ( Fig. 23H).

Etymology — The specific epithet honours the late Professor Jochen Heinrichs (1969–2018) of Munich, Germany, with whom we discussed the fossils and who expressed excitement when we discovered the first Selaginella in Kachin amber.