Scolecopteris oxydonta sp. nov., a new marattialean fern from the early Permian Wuda Tuff Flora

A marattialean fern with organically connected fertile and vegetative parts is described from the early Permian Wuda Tuff Flora in Inner Mongolia, China. The tripinnate fronds have typical pecopterid vegetative pinnules but do not match any known Pecopteris species. The fertile pinnules are distinctly different from the vegetative ones, with an extended margin that forms long lobes, bending abaxially to cover the synangia. Each fertile pinnule bears 7–10 ovate, pedicellate synangia arranged abaxially in a single row to either side of the midvein, with each synangium composed of 3–4 elongate sporangia. The sporangium wall is three-layered, with the outermost layer differentiated into four areas peripherally to provide differing mechanical strengths and facilitate dehiscence. In situ spores are trilete and 39–45 μm in diameter. These combined characteristics place the studied fern in the Scolecopteris Minor group of the Psaroniaceae family. The new species, Scolecopteris oxydonta sp. nov., exhibits many evolutionarily advanced traits such as modified fertile pinnules, unvascularized pedicels, differentiated sporangium walls, and a specialized opening mechanism. However, S. oxydonta sp. nov. also retains evolutionarily primitive traits including relatively large spores. S. oxydonta sp. nov. represents the fourth Scolecopteris species recognized from the Wuda Tuff Flora, adding to the growing body of evidence on the morphology and diversity of marattialean plants from the Permian of Cathaysia. We also consider preservational differences among the specimens and suggest that the composition and morphology of fertile pinnules produced closed microenvironments during early diagenesis that facilitated localized anatomical preservation.