A new species of Millerocaulis (Osmundaceae, Filicales) from the Middle Jurassic of China

A new species, Millerocaulis sinica, is established based on a specimen collected from Lanqi Formation (Middle Jurassic) near Changgao Town, Liaoning Province of China. The specimen represents a stem surrounded by a mantle of stipular petiole bases and adventitious roots. The stem, 11 × 12 mm in diameter, consists of ectophloic siphonostele with rare complete leaf gaps and a two-layered cortex containing 31-35 leaf traces. The pith consists of homogeneous parenchyma. The outer cortex is composed of sclerenchyma, and is thicker than the parenchymatous inner cortex. When departing from the stem, the leaf traces are flattened C-shaped, with an endarch protoxylem which bifurcates at the base of petiole. Sclerenchyma rings are heterogeneous. A crescent-shaped sclerenchymatous mass occurs in the concavity of petiolar vascular strands. A large sclerenchymatous mass and several small sclerenchymatous strands are aligned in each stipular expansion at the periphery of the specimen. M. sinica, which has thick band occupying abaxial semicircle of sclerenchyma rings as well as a heterogeneous sclerenchyma mass and several sclerenchyma strands scattered in the stipular expansions, is much closer to these of subgenus Osmunda than subgenus Plenasium and subgenus Osmundastrum in the genus Osmunda. Therefore, it is suggested that there is a possible phylogenetic relationship between M. sinica and subgenus Osmunda.