A New Genus of Betulaceae from the Oligocene of Western North America

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Abstract
An extinct genus of betulaceous fruit, Asterocarpinus perplexans (Cockerell) comb. nov., is described from three early Oligocene floras; the Florissant flora of Colorado, the lower John Day flora of Oregon, and the Grant flora of Montana. The fruit consists of a nutlet borne on an involucre of four to seven radiating wings. Based on chracters of the nutlet, Asterocarpinus is assigned to the Coryleae, but it is distinguished from all other coryleoid fruits by the morphology of the involucre. Asterocarpinus is associated with leaves of Paracarpinus fraterna (Lesquereux) comb. nov. in the Florissant flora and with leaves of P. chaneyi sp. nov. in the John Day flora. Similarities between these probable leaves of Asterocarpinus and those of extant Carpinus, together with similarities in the nutlets of Asterocarpinus, Carpinus, and Ostrya, indicate that these three genera may be closely related. Asterocarpinus, Carpinus, and Ostrya appear in the fossil record approximately synchronously and may have been derived from the same radiation of the Coryleae in the late Eocene and early Oligocene.

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