Selaginella amplexicaulis 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 : 210-212

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

Holotype: PB23160 [ Fig. 22], Nanjing Institute of Geology and Palaeontology, Chinese Academy of Sciences. – Fig. 2D; 22 (only specimen available).

Diagnosis — Strobilus compact, tetrastichous, quadrangular. Sporophylls monomorphic, imbricate, conduplicate, broadly ovate, strongly carinate, carina smooth, base biauriculate, apex acuminate, margins entire to erose, sporophyll-pteryx absent. Sporangia suborbicular.

Description — Rhizophores, branches and trophophylls not preserved. Strobilus compact, tetrastichous, quadrangular, 5.3 × 1.4 mm ( Fig. 22A). Sporophylls monomorphic, imbricate, conduplicate, 60 in only available strobilus, 0.7–0.9 × 0.4–0.6 mm, broadly ovate, strongly carinate, carina smooth, apex acuminate, base biauriculate, margins entire to erose, sporophyll-pteryx absent ( Fig. 2D; 22B, C). Epidermis of sporophylls composed of elongate cells, with long axes orientated uniformly parallel to carina. Sporangia suborbicular, 320–370 × 350–600 µm, with uniform isodiametric cells with thick anticlinal walls ( Fig. 22D). Microspores 20–25 µm in diam., probably immature, proximally psilate ( Fig. 22E).

Remarks — The sporophylls, which are acuminate at apex and entire to erose at the margins ( Fig. 2D; 22B, C), discriminate Selaginella amplexicaulis from all other Kachin Selaginella taxa with quadrangular strobili.

The morphology of the sporophylls and strobili of Selaginella amplexicaulis is very similar to that of four modern species, namely S. inaequalifolia (Hook. & Grev.) Spring , native to India, Myanmar and Thailand ( Dixit 1992; Fraser-Jenkins & al. 2017), S. ornithopodioides ( L.) Spring, endemic to Sri Lanka ( Dixit 1992; Fraser-Jenkins & al. 2017), S. trichoclada Alston , endemic to China ( Zhang & al. 2013) and S. willdenowii (Desv.) Baker , from China, India and SE Asia ( Dixit 1992; Fraser-Jenkins & al. 2017; Zhang & al. 2013). As the vegetative portion of S. amplexicaulis is not preserved, it is difficult to separate it from these extant species. However, there are subtle differences that can be used to distinguish the fossil-taxon. For instance, the extant species all have sporophylls that are obtuse, truncate or rounded at the base ( Alston 1932; Dixit 1992; Zhang & al. 2013), in contrast to the auriculate sporophylls of S. amplexicaulis ( Fig. 2D; 22B, C).

Etymology — The specific epithet is derived from the Latin words amplexus: clasping, and caulis: stem. It refers to the sporophyll bases clasping the strobilus stem.