Permineralized endocarps of Nyssa (Cornaceae) and another plant of uncertain affinity are described from the middle Miocene Yakima Canyon flora of central Washington State, USA. Some specimens are preserved within the chert matrix, while others have been weathered out to show three-dimensional features. Nyssa endocarps are 9-14 mm long, 5-8 mm wide, elliptical in outline, and typically have 4-12 longitudinally oriented ribs extending from a somewhat pointed base to a rounded apex. They have a curved, dorsal surface and a flat to convex ventral surface with an apical germination valve and appear unilocular. The other endocarp is subglobose to somewhat flattened, sometimes showing a pointed apex, 5.5 - 8 mm long, and 5-6 mm in diameter. In some specimens an additional outer layer 1.5-2 mm thick is preserved that appears like a halo of either fleshy or leathery tissue, which may represent the mesocarp. The endocarp is biloculate, with a single seed in each locule except for one specimen, which has two smaller seeds in one locule. Vascular strands are present along the central septum and in some specimens strands also occur around the periphery. Seeds are pyriform and slightly asymmetrical, 4 mm long, 3 mm wide in their major plane, and 1.5 mm wide in the minor plane.The seed coat is composed of three layers: an outermost dark epidermis, a central palisade layer and an inner region of poorly preserved cells. Some features of this biloculate drupaceous fruit suggest possible affinities with Cornaceae, but the vascularization and seed structure are not typical of this family. Based on available features, another possible relationship of the Yakima endocarps may be with Rhamnaceae.

Key words: Cornaceae, fossil endocarps, Miocene, Nyssa, Rhamnaceae