TCHEREPOVA, MARIA* and KATHLEEN B. PIGG. Department of Plant Biology, Arizona State University, Box 871601, Tempe, AZ 85287-1601 USA. - Permineralized Nyssa (Cornaceae) and additional endocarps of uncertain affinity from the middle Miocene Yakima Canyon flora, Washington State, USA.
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