Osmundastrum gvozdevae
Osmundastrum gvozdevae is an extinct species of royal fern identified from the Upper Bathonian deposits in the Mikhailovskii Rudnik locality, Kursk Region, in the European part of Russia. The species is known from coalified stems that have retained excellent cellular structure, making it an important discovery for the study of fossil Osmundaceae. It was formally described in 2019 and provisionally assigned to the extant genus Osmundastrum based on its anatomical similarities to modern representative.
Description
The species is known from small, coalified stems that have retained their internal cellular structure. The stem anatomy is characterized by an ectophloic dictyoxylic siphonostele, a common vascular configuration among ferns. The central pith consists of uniform prosenchymatous cells. One of the most distinctive features of Osmundastrum gvozdevae is the presence of endarch xylem in the leaf traces, with protoxylem strands that bifurcate as they traverse the outer cortex. This anatomy suggests a relatively advanced vascular architecture for a Middle Jurassic fern.Leaf bases in the fossil specimens possess stipular wings and contain horseshoe-shaped vascular bundles. These bundles exhibit two prominent masses of sclerenchyma located on the adaxial side of the concavity. Additionally, the sclerenchyma rings are heterogeneous, comprising thick-walled fibers that form a clearly defined abaxial arch and two lateral reinforcing masses. These combined traits bear a strong resemblance to the extant cinnamon fern, supporting the authors' decision to assign the fossil provisionally to the same genus.