Anatomically preserved specimens of globose staminate and pistillate inflorescences belonging to Platanaceae have been found in concretions at the Eocene Appian Way fossil locality on Vancouver Island, British Columbia, Canada. The structure of inflorescences and individual flowers, vascular architecture, and pollen morphology were examined. Flowers occur on globose unisexual heads and are supplied at their bases by branching pentagonal vascular traces. Flowers of staminate inflorescences have

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... well-developed perianth with at least two whorls of tepals. Five stamens with elongate anthers surround a single whorl of five (rarely four) free, nonfunctional carpels that are ovate in longitudinal section and roughly triangular in transverse section. In situ tricolpate pollen 16 mm in polar diameter is found in the anthers. This same pollen is found among the persistent styles of larger pistillate fructifications. The pistillate flowers are identical in structure to staminate flowers but have five fully developed carpels, and they lack stamens. Fruits are glabrous achenes up to 8 mm long. Staminate inflorescences compare most closely to those of Platananthus sp., but the regular cooccurrence of both stamens and rudimentary carpels in the same flower has not previously been reported in the fossil record, and, thus, these specimens have been placed in a new genus and species, Gynoplatananthus oysterbayensis. These platanaceous inflorescences add to our knowledge of the Appian Way flora and provide evidence that rudimentary carpels are an ancient feature within staminate flowers of Platanaceae.