A New Species of Millerocaulis (Osmundaceae) from the Lower Cretaceous of California.

A small permineralized osmundaceous stem has been collected from marine sediments of the Early Cretaceous (Aptian), Upper Chickabally Member of the Budden 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 the use of the cellulose acetate peel technique. The stem was erect, 11x13 mm in diameter, with a parenchymatous pith and two-layered cortex. The stele is an ectophloic siphonostele with 65-79 leaf traces in the stem per cross section. Leaf gaps are only produced in 13% of the 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 lining the adaxial concavity. Leaf bases have stipular wings with large patches of heterogeneous sclerenchyma and a few scattered strands outside of the heterogeneous sclerotic ring. Patches of sclerenchyma occur inside the ring and outside of the vascular tissues. Numerous diarch roots arise singly or doubly from the leaf traces as they depart the axis stele. Although the stem compares fairly closely to both Ashicaulis Tidwell and Millerocaulis Erasmus ex Tidwell emend. Tidwell, it is most similar to Millerocaulis. However, the combination of characters observed in our specimen differs from that of the seven known species of Millerocaulis. This stem is described as Millerocaulis embreei sp. nov. and is the youngest known species of the genus and the first to be found in the Northern Hemisphere.