Palaeocarpinus dakotensis sp.n. (Betulaceae: Coryloideae) and associated staminate catkins, pollen, and leaves from the Paleocene of North Dakota

Palaeocarpinus dakotensis Manchester, Pigg, et Crane sp.n. (Coryloideae, Betulaceae) is described from the Late Paleocene Almont and Beicegel Creek floras of North Dakota based on infructescences with associated staminate catkins, pollen, and leaves. The well-preserved, silica-permineralized specimens provide both anatomical and morphological data for this widely distributed genus of the Northern Hemisphere Paleogene. Characters that were previously unknown for the genus are described from anatomically preserved specimens, supporting earlier suggestions that Palaeocarpinus combines features found separately in the extant Coryleae and Carpineae. Features of Coryleae include infructescences composed of cymes with paired nuts, each enclosed within two highly dissected bracts of equal size quite similar to those of some species of modern Corylus, and staminate catkins with four to six bifurcate stamens per bract. Similarly, there are four bifurcate stamens per bract in extant Corylus and four to six in Ostryopsis, whereas more numerous stamens are found in Carpinus and Ostrya. Other features, however, are characteristic of the Carpineae, including external longitudinal ribs on bracts, many fruits per infructescence, and small, ribbed nuts with vascular bundles lying outside the endocarp. Pollen from the stamens of associated catkins is triporate with a scabrate exine and apparently lacks opercula on the apertures, as in Corylus. Simple, cordate-based elliptical leaves with pinnate, craspedodromous secondary veins and serrate margins referred to Corylites sp. are also found in association and are thought to represent the same coryloid plant. The appearance of Palaeocarpinus in the fossil record apparently predates that of extant genera in the Coryloideae, and it is likely that Palaeocarpinus-like plants were the forerunners of both Coryleae and Carpineae.