Fruit Morphology, Fossil History, and Biogeography of Paliurus (Rhamnaceae)

The genus Paliurus, recognized by its distinctive orbicular-winged fruit, is well represented in the fossil record of the Northern Hemisphere. Fruits assignable to Paliurus are known from the Tertiary of North America, Europe, and Asia, while extant species are limited to Eurasia. We examined variation in fruit morphology among extant species as a basis for interpreting fossil fruits. Although Paliurus fruits are diverse in size, shape, and sculpture, there are few consistent criteria for demarcating species. On the basis of morphometric analysis, we recommend synonymy of most fossil fruits under the name Paliurus favonii. New records for this species are reported from the Eocene and Miocene of North America, and a distinctive new species from the Middle Eocene of North America, Paliurus clarnensis, is introduced. The genus ranges from the Middle Eocene to Late Miocene in North America, the Late Eocene to Pleistocene in Asia, and from the Oligocene to Pliocene in Europe. The fossil record indicates range expansion over the Northern Hemisphere during the Eocene and Miocene, possibly via high latitude migratory routes, followed by dramatic range contraction near the close of the Miocene, including extinction from central Asia and North America.