Selaginella konijnenburgiae 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 : 215-216

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

Holotype: GZG. BST.22003 [ Fig. 24], Geoscientific Collection of the University of Göttingen. – Fig. 2F; 24 (only specimen available).

Diagnosis — Axes compressed. Trophophylls dimorphic. Dorsal trophophylls distant, adpressed, somewhat conduplicate, oblong-lanceolate, slightly carinate, base truncate, apex attenuate to aristate, margins entire to serrulate-denticulate. Ventral trophophylls mostly symmetric, sometimes asymmetric, distant, spreading, ascending, oblong-ovate, non-carinate, base with basiscopic side rounded, acroscopic side truncate, apex obtuse, margins serrulate. Strobilus terminal, tetrastichous, quadrangular. Sporophylls monomorphic, imbricate, broadly ovate, slightly carinate, base rounded, apex attenuate to aristate, margins serrulate-denticulate, sporophyll-pteryx absent. Sporangia suborbicular, a single considerably larger sporangium situated at base of strobilus. Microspores proximally rugulate.

Description — Rhizophores not preserved. Axes compressed. Trophophylls dimorphic ( Fig. 24H, I). Axillary trophophylls not preserved. Dorsal trophophylls distant, adpressed, somewhat conduplicate, 0.5–0.9 × 0.1–0.3 mm, oblong-lanceolate, slightly carinate, base truncate, apex attenuate to aristate, margins entire to serrulate-denticulate, teeth ≤ 10 µm long. Ventral trophophylls mostly symmetric, sometimes asymmetric, distant, spreading, ascending, 1.5–2.7 × 0.4–0.9 mm, oblong-ovate, non-carinate, base with basiscopic side rounded, acroscopic side truncate, apex obtuse, margins serrulate, teeth ≤ 10 µm long ( Fig. 24H, I). Epidermis of dorsal and ventral trophophylls composed of elongate cells, with long axes orientated uniformly parallel to long axis of trophophyll ( Fig. 24J). Strobilus terminal, tetrastichous, quadrangular, 5.6 × 1.1 mm ( Fig. 24A, B). Sporophylls monomorphic, imbricate, 48 in only available strobilus, 0.9–1.1 × 0.4–0.6 mm, broadly ovate, slightly carinate, base round- ed, apex attenuate to aristate, margins serrulate-denticulate, teeth 10–25 µm long, sporophyll-pteryx absent ( Fig. 2F; 24C, D, F, G). Epidermis of sporophylls is composed of elongate cells, with long axes orientated uniformly parallel to long axis of sporophyll ( Fig. 24E). Sporangia suborbicular, (300–)460–500 × (260–)280–340 µm, a single considerably larger sporangium situated at base of strobilus 900 × 800 µm, with uniform isodiametric cells with thick anticlinal walls. Microspores 25–30 µm in diam., proximally rugulate ( Fig. 24K).

Remarks — The presence of a basal sporangium (presumably a megasporangium), protruding and conspicuously larger than all other sporangia, separates Selaginella konijnenburgiae from all other Selaginella inclusions with quadrangular strobili, with the exception of S. heinrichsii . The latter species differs from S. konijnenburgiae in its distant sporophylls, which are exauriculate ( Fig. 2E). In contrast, S. konijnenburgiae has imbricate sporophylls with a rounded base ( Fig. 2F).

Three extant species are somewhat similar to the fossil morphology, namely Selaginella davidii Franchet , endemic to China ( Zhang & al. 2013), S. kraussiana (Kunze) A. Braun , from Macaronesia and tropical and S Africa ( Quansah 1986; Zhang & al. 2013) and S. remotifolia Spring , native to India, China, Indonesia, Japan, Nepal and the Philippines ( Van Alderwerelt van Rosenburgh 1915; Dixit 1992; Zhang & al. 2013; Fraser-Jenkins & al. 2017; Shalimov & al. 2019). These species share with S. konijnenburgiae the presence of ovate-lanceolate, long-acuminate or aristate, denticulate dorsal trophophylls, combined with the presence of quadrangular strobili, with ovate, monomorphic sporophylls that are attenuate, apically aristate or acuminate and serrulate or denticulate ( Van Alderwerelt van Rosenburgh 1915; Dixit 1992; Zhang & al. 2013; Shalimov & al. 2019). However, the three extant species differ from the fossil in having mostly acute ventral trophophyll margins ( Van Alderwerelt van Rosenburgh 1915; Dixit 1992; Zhang & al. 2013; Shalimov & al. 2019), in contrast to the obtuse ventral trophophylls of the fossil. Selaginella kraussiana has a densely denticulate carina, whereas S. konijnenburgiae has a smooth carina on the abaxial surface of the sporophylls. Additionally, S. davidii , S. kraussiana and S. remotifolia have microspores with an echinate proximal surface ( Quansah 1986; Zhou & al. 2015a), whereas S. konijnenburgiae has microspores with a rugulate proximal surface ( Fig. 24K).

Etymology — The specific epithet honours Professor Johanna H. A. van Konijnenburg-van Cittert (Leiden and Utrecht), for her contributions to the knowledge of fossil free-sporing vascular plants, including Selaginella .