Selaginella patrickmuelleri 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 : 198-200

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

Holotype: GZG. BST.22000 [ Fig. 13], Geoscientific Collection of the University of Göttingen. – Fig. 1G; 13 (only specimen available).

Diagnosis — Strobilus terminal, compact, bilateral, dorsiventrally complanate. Dorsal sporophylls close, ascending, conduplicate, ovate-lanceolate, carinate, apex acute, margins dentate; sporophyll-pteryx incomplete, slightly dentate. Ventral sporophylls imbricate, adpressed, peltate, broadly ovate, strongly carinate, apex attenuate, base rounded, margins sparsely long ciliate. Sporangia suborbicular. Megaspores proximally rugulate-reticulate. Microspores distally and proximally rugulate.

Description — Rhizophores, branches and trophophylls not preserved. Strobilus terminal, compact, bilateral, dorsiventrally complanate, 3.5 × 2 mm ( Fig. 13A). Sporophylls dimorphic. Dorsal sporophylls close, ascending, spreading, 13 in only available strobilus, 0.9–1.3 × 0.3–0.6 mm, conduplicate, ovate-lanceolate, carinate, base not seen, apex acute, margins dentate, teeth 25–40 µm long ( Fig. 1G; 13B, C); sporophyll-pteryx incomplete, slightly dentate, with teeth similar in size to those of margins ( Fig. 1G; 13B, C). Ventral sporophylls imbricate, adpressed, peltate, 11 in only available strobilus, 0.8–1.1 × 0.4–0.5 mm, broadly ovate, strongly carinate, base rounded, apex attenuate, margins widely spaced long ciliate, cilia 75–125 µm long ( Fig. 1G; 13D). Epidermis of ventral sporophylls with elongate cells, with long axes orientated uniformly parallel to carina ( Fig. 13D). Sporangia suborbicular, 280–380 × 440–500 µm, composed of uniform isodiametric cells with thick anticlinal walls ( Fig. 13E). Megaspore (only one preserved) c. 200 µm in diam., proximally rugulate-reticulate ( Fig. 13F). Microspores 25–30 µm in diam., distally and proximally rugulate ( Fig. 13G, H).

Remarks — Vegetative leaves are not preserved in this fossil, but we presume that Selaginella patrickmuelleri possessed resupinate strobili (see remarks under S. minutissima ).

Among the fossil-taxa with bilateral resupinate strobili that have a sporophyll-pteryx in the dorsal sporophylls and ventral sporophylls with long-ciliate margins, this species closely resembles Selaginella wangxinii . They both are characterized by close, ovate-lanceolate dorsal sporophylls, which are acute at the apex and dentate at the margins, and possess a dentate sporophyll-pteryx and broadly ovate ventral sporophylls, which are attenuate at the apex, sparsely ciliate at the margins and strongly carinate. However, the two taxa differ from each other in the size of the strobili, the shape of the sporophyll-pteryx and the ornamentation of the megaspores. Selaginella patrickmuelleri has strobili less than 4 mm long, dorsal sporophylls with an incomplete sporophyll-pteryx and megaspores rugulate-reticulate in the proximal surface ( Fig. 1G; 13B, C, F), whereas S. wangxinii is characterized by strobili 5–6 mm long, dorsal sporophylls with a nearly complete sporophyll-pteryx and megaspores proximally echinate ( Fig. 1H; 14D, F, J).

Identification of extant Selaginella species is usually based on combinations of characters from both the vegetative and reproductive parts of the plant. As the vegetative part of this fossil remains unknown, we found several extant species with morphological similarities to the fossil. Among the Asian, Australasian and Pacific species of Selaginella , 13 taxa closely resemble S. patrickmuelleri by having ovate-ciliate ventral sporophylls, including S. amblyphylla Alston from China, Myanmar and Thailand ( Zhang & al. 2013), S. bisulcata Spring from Bhutan, India, Indonesia (Java), Myanmar, Nepal, Thailand and Vietnam ( Zhang & al. 2013; Fraser-Jenkins & al. 2017; Shalimov & al. 2019), S. chaetoloma Alston , endemic to China ( Zhang & al. 2013), S. chrysocaulos (Hooker & Greville) Spring , widely distributed in China, India, Pakistan, Nepal and SE Asia ( Zhang & al. 2013; Fraser-Jenkins & al. 2017; Shalimov & al. 2019), S. chrysorrhizos Spring from Bhutan, India, Nepal and SE Asia ( Fraser-Jenkins & al. 2017; Shalimov & al. 2019), S. ciliaris (Retz.) Spring , widely distributed in Asia, Australasia and the Pacific islands ( Zhang & al. 2013; Fraser-Jenkins & al. 2017; Shalimov & al. 2019), S. elegantissima Warb. , endemic to Sulawesi ( Van Alderwerelt van Rosenburgh 1915), S. pennata (D. Don) Spring from China, India, Myanmar, Nepal and Thailand ( Zhang & al. 2013; Fraser-Jenkins & al. 2017; Shalimov & al. 2019), S. proniflora (Lam.) Baker , endemic to S and peninsular India ( Dixit 1992; Fraser-Jenkins & al. 2017), S. reticulata (Hook. & Grev.) Spring from Bangladesh, Bhutan, India, Myanmar and Nepal ( Dixit 1992; Fraser-Jenkins & al. 2017; Shalimov & al. 2019), S. subdiaphana (Wall. ex Hook. & Grev.) Spring , from Bhutan, India, Nepal and Pakistan ( Fraser-Jenkins & al. 2017; Shalimov & al. 2019, Irfan & al. 2021) and S. weinlandii Hieron. and S. zahnii Hieron. , both endemic to New Guinea ( Van Alderwerelt van Rosenburgh 1915). However, most of these taxa differ from the fossil in the shape of the sporophyll apex, the margins of the sporophyll-pteryx and sporophylls and the ornamentation of the mega- and microspores. For example, S. amblyphylla , S. bisulcata , S. chaetoloma , S. chrysocaulos , S. proniflora and S. reticulata have ciliate dorsal sporophylls (at least in the acroscopic side) and also a ciliate sporophyll-pteryx ( Dixit 1992; Zhang & al. 2013; Shalimov & al. 2019). Selaginella weinlandii and S. zahnii have dorsal sporophylls with ciliate margins, at least in the basal portions, and a ciliate sporophyll-pteryx ( Van Alderwerelt van Rosenburgh 1915). In contrast, S. patrickmuelleri has dentate dorsal sporophylls and a dentate sporophyll-pteryx ( Fig. 1G; 13B, C). Selaginella pennata has non-carinate ventral sporophylls ( Zhang & al. 2013) and verrucate megaspores ( Zhou & al. 2015a), whereas S. patrickmuelleri has strongly carinate ventral sporophylls and rugulate-reticulate megaspores ( Fig. 1G; 13D, F). Finally, the arrangement and shape of the sporophylls in S. chrysorrhizos , S. ciliaris , S. elegantissima and S. subdiaphana are very similar to those seen in the fossil. However, there are also some differences, in that S. ciliaris has a clearly ciliate sporophyll-pteryx ( Dixit 1992; Zhang & al. 2013; Johari & Singh 2017) and baculate microspores ( Zhou & al. 2015a). The sporophyll-pteryx of S. elegantissima is mostly entire or with a few sparse marginal teeth and its microspores are verrucate ( Van Alderwerelt van Rosenburgh 1915). Selaginella chrysorrhizos and S. subdiaphana have verrucate mega- and microspores ( Dixit 1992; Shalimov & al. 2019; Irfan & al. 2021). By contrast, the sporophyll-pteryx of the fossil is dentate and the microspores are usually rugulate ( Fig. 1G; 13B, C, H).

Etymology — The specific epithet honours Patrick Müller (Zweibrücken, Germany), for his generous support of our work and collaboration on Kachin amber inclusions over many years and for continuously making new amber inclusions available for study.