Paleoochna tiffneyi gen. et sp. nov. (Ochnaceae) from the late paleocene almont/beicegel creek flora, North Dakota, USA

Premise of research. Paleoochna tiffneyi gen. et sp. nov. is described from late Paleocene fossil fruits from Almont (Morton County) and Beicegel Creek (McKenzie County), North Dakota. On the basis of distinctive anatomical and morphological features, these fruits demonstrate strong taxonomic affinities to Ochna and other members of the family Ochnaceae but are distinct at the generic level. Methodology. Fossil fruits were studied with a combination of transmitted and reflected light microscopy from fractured surfaces and with scanning electron microscopy. Extant fruits were sectioned by freehand sectioning with a razor blade and studied with reflected and transmitted light microscopy. Pivotal results. The study documents the first known occurrence of Ochnaceae fruits in the fossil record. They occur as late Paleocene specimens from the Williston Basin of the Western Interior of North America. Specimens are anatomically preserved and provide critical morphological details of systematic value. Like many of the other plants from the well-known Almont/Beicegel Creek flora, Paleoochna has strong affinities to extant genera but cannot be placed in a modern taxon. Along with fossil leaves of Rhabdophyllum (Ochnaceae) of slightly younger age from southeastern North America, Paleoochna corroborates the presence of Ochna-like plants by the Paleogene in North America. Conclusions. The presence of the Ochnaceae, subfamily Ochnoideae, tribe Ochneae, subtribe Ochninae in the Almont/Beicegel Creek flora suggests that some families within Malpighiales were well established in the Western Interior Basin of North America by the late Paleocene. The presence of Paleoochna in the late Paleocene Williston Basin and of Rhabdophyllum leaves in the early Eocene Mississippian Embayment suggests an interesting biogeographic connection for the family between the Western Interior Basin and the Gulf Coast during the Paleogene.