Petrified plants from the cretaceous of the Kwanto mountains,central Japan. III. A polyxylic cycadean trunk,Sanchucycas gigantea gen. et sp. nov.

Sanchucycas gigantea gen. et sp. nov. is a fossil cycadophyte trunk from the Lower Cretaceous (Late Barremian—Early Aptian) Sebayashi Formation of the Sanchu area, Gunma Prefecture. It has polycyclic vascular bundles, pitted tracheids, uni- to hexaseriate rays, one or two large cross field pits, and mucilage sacs.Sanchucycas is most closely comparable withCycas andEncephalartos among living members of the Cycadales, but is distinct in its large number of xylem cylinders constituting a thick polyxylic wood, and in having mucilage sacs contrary to canals. This is the earliest record of polyxylic cycadean stems. Contributions from the Laboratory of Phylogenetic Botany, Chiba University no. 122.