Fossil Leaves and Fruits of Cercis L. (Leguminosae) from the Eocene of Western North America

Premise of research. The fossil record of Cercis L. needs to be understood in better detail as a basis for reconstructing the evolution for understanding the radiation of Caesalpinoideae. The genus can now be traced back to the late Eocene of western North America on the basis of fossil fruits and foliage from Oregon and Colorado. Pivotal results. We present a new occurrence of Cercis leaf fossils from Teater Road, Oregon (similar to 36 Ma), that conforms to the species Cercis parvifolia Lesquereux, previously recognized from Florissant, Colorado (similar to 34 Ma). Associated pods of Cercis herbmeyeri sp. n. represent the earliest confirmed fossil fruits of Cercis. In their indehiscent pods with a winglike flange along one margin, the fossils correspond to the main clade of Cercis rather than to the phylogenetically distinct extant species Cercis chingii. A review of other occurrences that we accept from the literature reveals that the genus was widespread in the Northern Hemisphere by the Miocene, although some earlier paleobotanical reports must be rejected. Conclusions. The fossil record indicates that Cercis was established by the late Eocene and had become widespread in the Northern Hemisphere by the Miocene. The late Eocene records have a lamina shape consistent with a mesic habitat but relatively small leaf size, which might indicate adaptation for drying conditions.