Herendeeniodoxa willistonensis gen. et sp. nov., Fossil Actinidiaceae Fruits and Seeds from the Late Paleocene of North Dakota, USA

Premise of research. Fossil fruits and seeds assignable to Herendeeniodoxa willistonensis Pigg, Ickert-Bond, DeVore & Flynn gen. et sp. nov. (Actinidiaceae) are described from the Late Paleocene (Tiffanian) Almont and Beicegel Creek localities in the Williston Basin, North Dakota, USA.Methodology. Fossil fruits and seeds occurring in silicified shale with external morphology were studied with reflected LM. Some specimens with detailed anatomical preservation were prepared by the cellulose acetate peel technique as modified for hydrofluoric acid, mounted on microscope slides, and digitally imaged with transmitted light. The holotype specimen and an isolated seed were studied with CT scanning. Extant fruits were imaged and prepared by free-hand sectioning with a razor blade, and others were prepared by standard techniques and studied with transmitted LM.Pivotal results. Based on fruit and seed morphology and anatomy, Herendeeniodoxa is assignable to Actinidiaceae but has a mosaic combination of features not found in extant genera of this family. General fruit shape and organization resemble those of Saurauia and Clematoclethra; however, seed morphology and seed coat anatomy are more like those of Actinidia, and seed coat anatomy also resembles that of Clematoclethra. This suggests that Herendeeniodoxa represents a mosaic taxon prior to, or during, the modern diversification of Actinidiaceae.Conclusions. Herendeeniodoxa willistonensis is the first fruit of Actinidiaceae to be recognized in the Late Paleocene of the Western Interior of North America. Herendeeniodoxa willistonensis provides information about fruits and anatomical seed structure for a group previously known mainly from its distinctive seed casts and compressions. The record suggests a North American/European origin for Actinidiaceae, as well as further early diversification into western North America in the Paleogene, then in Europe from the Eocene onward. The family appears in Asia by the Miocene. The current distribution is in Asia for Actinidia and Clematoclethra, whereas Saurauia is more widely distributed in tropical Asia, Oceania, and the Neotropics.