Stems of a New Osmundaceous Fern from the Middle Jurassic of Kursk Region, European Russia

Аннотация

New species of osmundaceous ferns, Osmundastrum gvozdevae sp. nov., is established on the basis of small coalified stems with preserved cellular structure, originated from the Upper Bathonian deposits of the Mikhailovskii Rudnik locality (Kursk Region, European Russia). Vascular tissues of the stem are represented by ectophloic dictyoxylic siphonostele; pith homogenous, comprising prosenchymatous cells only. Xylem of the leaf trace is endarch, with protoxylem strand, bifurcating when passes through the external part of an outer cortex. Leaf bases with stipular wings; their vascular bundles are horseshoe-shaped, with two sclerenchyma masses on the side of adaxial concavity. Sclerenchyma rings in the leaf bases are heterogeneous, thick-walled fibers form distinct abaxial arch and two lateral masses. The new species is provisionally assigned to the extant genus Osmundastrum C. Presl on the basis of the stem anatomical peculiarities.