Betula leaves and reproductive structures from the Middle Eocene of British Columbia, Canada

Abstract

Fossil angiosperm leaves from the Middle Eocene Allenby Formation, at One Mile Creek near Princeton, southern British Columbia, are described and assigned to Betula leopoldae Wolfe & Wehr. Morphological details of associated infructescences, fruits, staminate inflorescences, and pollen are also very similar to those of extant Betula. Based on association evidence and independently determined systematic relationships, we suggest that the vegetative and reproductive structures were produced by a single fossil species. Combined information from all the organs available suggests that this Eocene Betula is most closely related to species in section Eubetula, subsection Costatae of the extant genus. Material from One Mile Creek constitutes the earliest fully documented record of the genus Betula based on both vegetative and reproductive structures. In the context of the fossil history of the Betulaceae as a whole, it indicates that the two extant genera of the Betuleae, Alnus and Betula, were clearly differentiated by the Middle Eocene.