Cascadiacarpa spinosa gen. et sp. nov. (Fagaceae): castaneoid fruits from the Eocene of Vancouver Island, Canada

Abstract

Documenting the paleodiversity of well-studied angiosperm families serves to broaden their circumscription while also providing a time-specific reference point to mark the first occurrence of characters and appearance of lineages. More than 80 anatomically preserved specimens of spiny, cupulate fruits in various developmental stages have been studied from the Eocene Appian Way locality of Vancouver Island, British Columbia, Canada. Details of internal anatomy and external morphology are known for the cupules, fruits, and pedicels. Cupule spines branch and are often borne in clusters. Cupules lack clear sutures and are adnate to a single nut that is enclosed entirely with the exception of the apical stylar protrusion of the pistil. A central hollow cylinder of vascular tissue can be seen extending up the peduncle to the base of the fruit and along the inner wall of the cupule. The fruit has a sclerotic outer pericarp that grades into a parenchymatous mesocarp and a sclerotic endocarp lining the locules. Early in development, the two locules are divided by a thin septum to which the ovules are attached. Only one seed develops to maturity as evidenced by an embryo occupying the locule alongside an abortive apical ovule. Three-dimensional reconstructions of these fruits have allowed for comparisons to both extinct and extant fagaceous taxa. The Appian Way fruits are most similar to extant Castanopsis species (Fagaceae) but differ in having only two locules. Cascadiacarpa spinosa gen. et sp. nov. Mindell, Stockey et Beard is the first occurence of a bipartite gynoecium and earliest known occurrence of hypogeous fruits in Fagaceae. The appearance of Casacadiacarpa in the Eocene of British Columbia supports a Paleogene radiation of the family. The numerous derived characters of these fruits show that evalvate, spiny, single-fruited cupules of Fagaceae were present in the Paleogene of North America.