Cascadiacarpa exilissp. nov.: new fruits of Fagaceae from the Eocene of British Columbia

Abstract

More than 800 permineralized fagaceous fruits have been studied from the Eocene Appian Way locality of Vancouver Island, British Columbia. These cupulate nuts are the most common fruits preserved at the locality. They occur in calcareous concretions and were studied using the cellulose acetate peel technique. Cupules are borne on a spiny stalk and are broadly ovate in both longitudinal and transverse section. Cupules are evalvate and have both branching and simple spines. A single, ovoid, sclerotic nut is enclosed entirely by the cupule, except at the apex, where a stylar protrusion is free from any surrounding tissues. The nut is bilocular with a glabrous endocarp lining. At maturity, a single seed occupies the locular cavity. The embryo is straight and no endosperm is evident. The single-fruited, spiny cupule is most similar to fruits of Fagaceae subfamily Castaneoideae. Bicarpellate fruits and a glabrous endocarp place them within the fossil genus Cascadiacarpa; however, they differ from Cascadiacarpa spinosa in nut wall anatomy, cupule ornamentation, shape, and size. Fruits of Cascadiacarpa exilis sp. nov. are compared with spiny, small compression and impression fossil fruits from the Eocene Taneum Creek locality of Washington State. The characters of the Washington State fossils overlap with those observed in the anatomically preserved Appian Way cupulate fruits and, as such, may represent compression and impression fossils of the same genus. The permineralized fruits document that evalvate, spiny, cupulate nuts of Fagaceae were present and common in the Eocene of western North America.