Palaeocarpinus aspinosa Sp. Nov. (Betulaceae) from the Paleocene of Wyoming, U. S. A.

A new species of Palaeocarpinus Crane (Betulaceae) is recognized from the Paleocene of southwestern Wyoming that extends the concept of the genus to include fruits with nonspiny bracts. Fruits of P. aspinosa sp. nov. are borne in pairs on an elongate infructescence, each fruit enclosed by two equal bracts that are entire-margined to serrate but not dissected or spiny. Associated staminate catkins contain well-preserved pollen that is not only triporate, but commonly tetra- to pentaporate. The pollen exine is tectate-granular, with spinulate ornamentation. Co-occurring betulaceous leaves are similar to those of P. joffrensis Sun et Stockey from Canada and P. orientalis from China and to leaves of extant Corylus. The associated infructescences, leaves, and staminate inflorescences with in situ pollen facilitate detailed reconstruction of this extinct species and provide a clearer understanding of the genus and its relation to extant genera. Palaeocarpinus aspinosa, with its nonspiny fruit bracts and multiporate pollen, adds to our understanding of the morphological diversity present in this widespread early Tertiary genus. The nondissected bracts may have been effective for wind and water dispersal whereas other species with spiny burrlike bracts may have been dispersed by furry animals.