Selaginella villosa 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 : 206

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

Holotype: GZG.BST. 22028 [ Fig. 17], Geoscientific Collection of the University of Göttingen. – Fig. 1J; 17 (only specimen available).

Diagnosis — Axes compressed. Trophophylls dimorphic. Axillary trophophylls symmetric, oblong, non-carinate, base rounded, apex acute, distal and medial margins denticulate, proximal margins ciliate. Dorsal trophophylls close to distant, adpressed, symmetric, oblong-ovate or elliptic, slightly carinate, base decurrent, apex, margins mostly denticulate, ciliate only on proximal acroscopic side. Ventral trophophylls close to distant, spreading, symmetric, oblong, non-carinate, base rounded to truncate, apex acute or less frequently obtuse, margins mostly dentate-denticulate, proximal acroscopic margin ciliate. Strobili terminal, compact, bilateral, dorsiventrally complanate, resupinate. Sporophylls dimorphic. Dorsal sporophylls close, ascending, asymmetric, ovate-lanceolate, non-carinate, base inequilateral, basiscopic side straight, acroscopic side rounded, apex acute to attenuate, basiscopic margin serrulate, acroscopic margin ciliate; sporophyll-pteryx incomplete, broadly enlarged at base forming an auricle, ciliate on distal margins and dentate-denticulate in auricle. Ventral sporophylls close, conduplicate, ovate, carinate, base decurrent, apex acuminate, margins long-ciliate, dentate in apical portion. Sporangia suborbicular. Microspores distally and proximally rugulate.

Description — Rhizophores not preserved. Axes compressed. Trophophylls dimorphic ( Fig. 17A, B, J). Axillary trophophylls symmetric, c. 0.6 × 0.2 mm, oblong, non-carinate, base rounded, apex acute, distal and medial margins denticulate, proximal margins ciliate, teeth 10–20 µm long, cilia 50–80 µm long ( Fig. 17J). Dorsal trophophylls close to distant, adpressed, symmetric, 0.5–0.9 × 0.2–0.4 mm, oblong-ovate or elliptic, slightly carinate, base decurrent, apex acuminate, margins mostly denticulate, ciliate only on proximal acroscopic margin, teeth 15–20 µm long, cilia 50–70 µm long ( Fig. 17I). Ventral trophophylls close to distant, spreading, symmetric, 1.2–1.7 × 0.4–0.5 mm, oblong, non-carinate, base rounded to truncate, apex acute or less frequently obtuse, margins mostly dentate-denticulate, proximal acroscopic margin ciliate, teeth 10–30 µm long, cilia 50–150 µm long ( Fig. 17J). Strobili terminal, compact, bilateral, dorsiventrally complanate, resupinate, 2.6–3.0 × 1.9–2.3 mm ( Fig. 17A, B). Sporophylls dimorphic. Dorsal sporophylls close, ascending, asymmetric, 7 or 8 per strobilus, 1.4–1.6 × 0.3–0.4 mm, ovate-lanceolate, non-carinate, base inequilateral, basiscopic side straight, acroscopic side rounded, apex acute to attenuate, basiscopic margin serrulate, acroscopic margin ciliate, teeth 10–20 µm long, cilia 150–320 µm long ( Fig. 1J; 17C, D); sporophyll-pteryx incomplete, broadly enlarged at base forming an auricle, ciliate on distal margins and dentate-denticulate in auricle, teeth 10–30 µm long, cilia <100 µm long ( Fig. 1J; 17C). Epidermis of dorsal sporophylls formed by uniform isodiametric cells. Ventral sporophylls close, conduplicate, 7–9 per strobilus, 0.7–1.1 × 0.4–0.5 mm, ovate, carinate, base decurrent, apex acuminate, margins long-ciliate, dentate in apical portion, teeth 20–50 µm long, cilia 70–450 µm long ( Fig. 1J; 17E). Epidermis of ventral sporophylls with elongate cells, with long axes orientated uniformly parallel to carina. Sporangia suborbicular, 300–450 × 450–480 µm, composed of uniform isodiametric cells with thick anticlinal walls ( Fig. 13F). Microspores 30–35 µm in diam., distally and proximally rugulate ( Fig. 17G, H).

Remarks — Among the Kachin Selaginella inclusions detailed in this study, S. villosa most closely resembles S. ciliifera because both taxa have ciliate trophophylls and sporophylls. However, differences in the shape of sporophyll-pteryx of the dorsal sporophylls and in the apex of ventral sporophylls discriminate these two taxa (see remarks under S. ciliifera for details).

The extant Selaginella albociliata , S. apoensis , S. longiciliata and S. macroblepharis share with the fossil the general morphology of the dorsal and ventral sporophylls that are conspicuously ciliate, particularly the ventral sporophylls with acuminate apices ( Van Alderwerelt van Rosenburgh 1915; Wang 1990). However, the fossil differs from these taxa in that it has rugulate microspores ( Fig. 17G, H), rather than verrucate or smooth microspores as in the extant species ( Van Alderwerelt van Rosenburgh 1915; Jermy & Holmes 1998; Wang 1990). Furthermore, S. albociliata and S. apoensis have longer strobili ( 6–20 mm long) ( Van Alderwerelt van Rosenburgh 1915; Wang 1990), whereas S. villosa produces strobili only up to 3 mm long.

Etymology — The specific epithet is derived from the Latin word villosus: having many long, weak hairs. It refers to the numerous long ciliae, especially those seen on the ventral sporophylls.