Stockeystrobus gen. Nov. (Cupressaceae), and the evolutionary diversification of sequoioid conifer seed cones

Abstract

An anatomically preserved seed cone from Late Cretaceous (Santonian-Coniacian) sediments of the Yezo Group on the Japanese Island of Hokkaido documents additional diversity among sequoioid conifers, and reveals previously unknown mechanisms for pollination and post-pollination seed enclosure in the conifer family Cupressaceae. The cylindrical seed cone of Stockeystrobus interdigitata gen. et sp. nov., consists of a central axis bearing helically arranged bract-scale complexes. Individual complexes are tightly packed and peltate in form, with completely fused bracts and scales. Peltate heads of adjacent complexes are attached to each other by elongated interdigitating epidermal trichomes. Each complex bears 6-8 inverted seeds on the adaxial surface of the inside of the peltate bract-scale complex head. Seeds occur in a single row, are roughly disk shaped, with broad wings in the major plane of symmetry. The nucellus is attached to the seed integument at the chalaza and free distally, with a convoluted apex. This cone reveals greater diversity of sequoioid reproductive biology than is represented among living species, and demonstrates that completely enclosed cones with well protected seeds were produced by Late Cretaceous fossil conifers of the Cupressaceae.