Extinct Anacardiaceous Samaras and Sumac-Like Leaves from the Eocene of Western North America

Abstract

An extinct kind of asymmetric samara occurs in the Eocene of Colorado, Utah, and Wyoming. The distinctive winged fruits were attributed to Anacardiaceae by Roland Brown in the 1920s and 1930s and were placed in the fossil genus Anacardites. However, that generic name, based on leaves from the Oligocene of France described a century earlier by Saporta, is inappropriate for these fruits. The samaras, which were not previously described in detail, are pedicellate, with a scar of hypogynous perianth and disk, and are nonschizocarpic, with an elliptical single-seeded endocarp and a lateral wing supplied with arching subparallel venation. We recognize these fruits as an extinct genus, Barkleya gen. nov. Although morphologically unique, the fruits share some characters in common with samaroid fruits of subfamily Anacardioideae, including Amphipterygium, Faguetia, Loxopterygium, Orthopterygium, and Schinopsis. We also provide an emended diagnosis for Rhus nigricans foliage and speculate, on the basis of co-occurrence and shared familial relationships, that the fruits of Barkleya schinoloxus (RW Brown) comb. nov. were produced by the same plant, which was a common element of the early to middle Eocene Green River flora.