ASHICAULIS BEIPIAOENSIS SP NOV., A NEW OSMUNDACEOUS FERN SPECIES FROM THE MIDDLE JURASSIC OF LIAONING PROVINCE, NORTHEASTERN CHINA

A new structurally preserved fern rhizome species, Ashicaulis beipiaoensis (Osmundaceae), is described from the Middle Jurassic Tiaojishan Formation in Beipiao City, Liaoning Province, northeastern China. The rhizome, with a maximum diameter of 4.0-4.5 cm, is composed of a homogeneous parenchymatous pith, an ectophloic-dictyoxylic siphonostele, a two-layered cortex, and a mantle of adventitious roots and petiole bases. The xylem cylinder consists of 13-16 xylem strands. The petiole base is characterized by a homogeneous sclerotic ring and a crescent-shaped sclerenchyma mass in the vascular bundle concavity. One large homogeneous sclerenchyma mass, accompanied by several smaller thick-walled fiber clusters, occurs in the petiolar stipular wings. Comparisons of anatomical features suggest that A. beipiaoensis sp. nov. shows distinct differences when compared to previously reported fossil and living osmundaceous taxa but bears close similarities to Osmunda shimokawaensis from the Middle Miocene of Hokkaido, Japan. The new species and O. shimokawaensis may represent an extinct branch in the Osmundaceae evolutionary tree. The fossil species of A. beipiaoensis provides further information for understanding the development and geological occurrences of osmundaceous rhizomes in the Northern Hemisphere.