Two new leptosporangiate ferns from in situ volcanic ash of the Whetstone Horizon (Kladno Formation, Pennsylvanian), Pilsen Basin, Czech Republic.

Abstract

A new leptosporangiate fern genus, Discosoropteris, is recognized and two species circumscribed from the Duckmantian-age Kamenný Újezd locality of the Pilsen Basin, Central Bohemia based upon tripinnate fronds preserved in the Bělka tuff. The sphenopterid pinnules bear massive disc-shaped sori, either on the laterals or midvein, that contain up to 80 annulate sporangia. The trilete microspores vary from laevigate, to microgranulate, microspinate, or finely reticulate and, thus, are comparable to both Leiotriletes and Granulatisporites. This variance is deemed most likely to reflect different stages of spore maturation. The cuticle preserves anomocytic stomata on the pinnae and a dense indumentum of multicellular uniseriate trichomes on the rachis. Trichomes are also dense within the sori where they appear to approximate the utilities of an indusium, whether for limiting environmental exposure or access to herbivores. These compression fossils preserve some traces of internal anatomy, including scalariform tracheids and bundle sheath cells that show signs of puncture-feeding herbivory. The bearing stem is unknown but preservation of the fronds within the tuff suggests they were elevated on a short, upright, self-supporting axis. Comparisons are drawn with other Carboniferous taxa, particularly Discopteris; review of the complex history of these alternatives suggests Discosoropteris is best left as incertae sedis within the basal leptosporangiate ferns rather than adding to the confusion by attempting a family-level assignment at this time.