A new species of Millerocaulis (Osmundaceae) from the lower Cretaceous of California

A small permineralized osmundaceous stem has been collected from marine sed iments of the Early Cretaceous (Aptian), Upper Chickabally Member of the Bu dden Canyon Formation near Ono, California. The specimen, 8.5 cm long and 5 .4 cm wide, represents a stem surrounded by a mantle of stipular leaf bases and adventitious roots. A large number of sections were studied through th e use of the cellulose acetate peel technique. The stem was erect, 11 x 13 mm in diameter, with a parenchymatous pith and two-layered cortex. The stel e is an ectophloic siphonostele with 65-79 leaf traces in the stem per cros s section. Leaf gaps are only produced in 13% off he departing traces. Most leaf traces have "delayed" gaps or completely lack leaf gaps. Leaf traces are C-shaped, endarch, with one protoxylem strand, and have sclerenchyma li ning the adaxial concavity. Leaf bases have stipular wings with large patch es of heterogeneous sclerenchyma and a few scattered strands outside of the heterogeneous sclerotic ring. Patches of sclerenchyma occur inside the rin g and outside of the vascular tissues. Numerous diarch roots arise singly o r doubly from the leaf traces as they depart the axis stele. Although the s tem compares fairly closely to both Ashicaulis Tidwell and Millerocaulis Er asmus ex Tidwell emend. Tidwell, it is most similar to Millerocaulis. Howev er, the combination of characters observed in our specimen differs from tha t of the seven known species of Millerocaulis. This stem is described as Mi llerocaulis embreei sp. nov, and is the youngest known species of the genus and the first to be found in the Northern Hemisphere.