Selaginella ohlhoffiorum 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 : 192-195

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

Holotype: GZG. BST.21966a [ Fig. 8A–C], Geoscientific Collection of the University of Göttingen. – Fig. 1D; 8–10 (three specimens available).

Diagnosis — Axes compressed. Trophophylls dimorphic. Axillary trophophylls symmetric, oblong-lanceolate, apex acute to obtuse, base rounded, margins slightly serrate. Dorsal trophophylls distant, slightly asymmetric, oblong, non-carinate, aristate at apex, serrulate-denticulate at margins. Ventral trophophylls distant, symmetric, oblong to rarely ovate, non-carinate, base truncate, apex obtuse to rounded, margins serrate-serrulate. Strobili terminal, bilateral, dorsiventrally complanate, resupinate. Sporophylls dimorphic. Dorsal sporophylls close to distant, ovate-lanceolate, slightly carinate, apex acute to obtuse, margins serrulate-denticulate; sporophyll-pteryx incomplete, with serrulate margins. Ventral sporophylls close to distant, broadly ovate, base decurrent, slightly carinate, apex sharply acuminate, margins denticulate. Sporangia orbicular. Megaspores distally and proximally reticulate. Microspores distally and proximally rugulate.

Description — Rhizophores not preserved. Axes compressed. Trophophylls dimorphic ( Fig. 8A; 10A, B). Axillary trophophylls symmetric, somewhat conduplicate, 0.9–1.6 × 0.3–0.4 mm, oblong-lanceolate, non-carinate, base rounded, apex acute to obtuse, margins slightly serrate, teeth 8–20 µm long. Dorsal trophophylls distant, adpressed, somewhat asymmetric, 0.9–1.1 × 0.3–0.5 mm, oblong, non-carinate, base not seen, apex aristate, margins serrate-dentate, teeth 8–20 µm long. Ventral trophophylls distant, spreading, symmetric, 1.2–1.7 × 0.5–0.8 mm, oblong to rarely ovate, non-carinate, base truncate, apex obtuse to rounded, margins serrate-serrulate, teeth 8–35 µm long. Epidermis of dorsal and ventral trophophylls with uniform polyhedral cells ( Fig. 8D). Strobili terminal, bilateral, dorsiventrally complanate, resupinate, 3.5–6.8 × 1.8–2.2 mm ( Fig. 8A; 9A–C). Sporophylls dimorphic. Dorsal sporophylls close to distant, spreading, conduplicate, 10 or 11 per strobilus (– 26 in GZG. BST.22026), 0.8–1.2 × 0.5–0.7 mm, ovate-lanceolate, slightly carinate, base not seen, apex acute to obtuse, margins serrulate-denticulate, teeth 10–20 µm long ( Fig. 1D; 8C; 9D); sporophyll-pteryx incomplete, with serrulate margins similar to those along sporophyll margins ( Fig. 1D; 8C; 9D). Epidermis of dorsal sporophylls composed of uniform polyhedral isodiametric cells. Ventral sporophylls close to distant, spreading, slightly conduplicate, symmetric, 10 or 11 per strobilus (– 26 in GZG. BST.22026), 1.2–1.4 × 0.3–0.4 mm, broadly ovate, slightly carinate, base decurrent, apex sharply acuminate, margins denticulate, teeth 5–12 µm long ( Fig 1D; 8B; 9H). Epidermis of ventral sporophylls composed of elongate cells, with long axes orientated uniformly parallel to long axis of sporophyll ( Fig. 9H). Sporangia orbicular, 420–740 × 440–800 µm, composed of uniform isodiametric cells with thick anticlinal walls ( Fig. 9E). Megaspores 350–400 µm in diam., distally and proximally reticulate ( Fig. 8F–H). Microspores numerous, 30–40 µm in diam., distally and proximally rugulate ( Fig. 8E; 9F, G).

Remarks — Among the Selaginella amber inclusions with bilateral strobili, S. ohlhoffiorum is very similar morphologically to S. grimaldii and S. cretacea . However, the latter taxa differ from the former in the shape of the ventral trophophylls, strobilus size and sporangium shape (see description and remarks under S. grimaldii for details).

Several extant species, such as Selaginella decipiens , S. miniatospora , S. monospora , S. tenera and S. trichophylla , share with S. ohlhoffiorum the ovate and denticulate ventral sporophylls and the ovate or lanceolate dorsal sporophylls possessing denticulate margins and bearing a denticulate sporophyll-pteryx in the adaxial surface ( Dixit 1992; Zhang & al. 2013). Selaginella monospora and S. trichophylla have a complete sporophyll-pteryx in the dorsal sporophylls ( Zhang & al. 2013) and verrucate megaspores and microspores ( Zhou & al. 2015a), whereas the sporophyll-pteryx is incomplete in S. ohlhoffiorum ( Fig. 1D; 8C; 9D), and the taxon produced reticulate megaspores ( Fig. 8F, G) and rugulate microspores ( Fig. 8E; 9F, G). Selaginella decipiens is distinguished from the fossil by its asymmetric ventral trophophylls, with the acroscopic base strongly enlarged, broader, sometimes overlapping the branches ( Zhang & al. 2013), and its verrucate megaspores ( Zhou & al. 2015a). In contrast, S. ohlhoffiorum has symmetric ventral trophophylls ( Fig. 8A; 10B), with a truncate base, and reticulate megaspores ( Fig. 9F, G). Selaginella tenera and S. miniatospora have ventral trophophylls acute to subacute at the apex, asymmetric with a dilated acroscopic base, conspicuously aristate ventral sporophylls and papillate or verrucate megaspores ( Dixit 1992). In comparison, the fossil is characterized by distinctly obtuse to rounded ventral trophophylls ( Fig. 8A; 10B), acuminate ventral sporophylls ( Fig. 8B; 9H) and reticulate megaspores ( Fig. 8F, G).

Etymology — The specific epithet honours Astrid, Mara and Rainer Ohlhoff (Saarbrücken, Germany), who discovered the inclusions in amber specimen GZG. BST.21966 and generously made them available for study.

Additional specimens studied — GZG. BST.21966b–e and GZG. BST.22026, Geoscientific Collection of the University of Göttingen ( Fig. 9), Patrick Müller Amber Collection BuB2711. Amber specimen GZG. BST.21966 has been cut into five pieces ( GZG. BST.21966a to GZG. BST.21966e) to better access the individual plant fragments, megaspores and microspores ( Fig. 8; 10).