Arctic Walnuts! Nuts of Juglans (Juglandaceae) from the Middle Eocene of Axel Heiberg Island, Northern Canada.

Three new fossil species of walnuts, Juglans eoarctica sp. nov., J. nathorstii sp. nov., and J. cordata sp. nov., are described on the basis of nuts recovered from the middle Eocene fossil forests of Axel Heiberg Island in the Canadian Arctic Archipelago. These represent the most northerly occurrence of Juglans and are among the oldest records of Juglans to date. The Axel Heiberg Island walnuts conform to the sections Rhysocaryon and Cardiocaryon and, together with the contemporaneous midlatitude fossil species J. clarnensis Scott, imply the establishment of two distinct Juglans lineages prior to the middle Eocene. Climatic cooling, leading ultimately to Pleistocene glaciation, has transformed high-latitude vegetation and resulted in the American/Eurasian disjunct distribution found in many north temperate families, of which Juglans is typical. With three coexisting species in the Axel Heiberg Island fossil forests, it is clear that Juglans was an important component of this ancient polar landscape and played a significant role in the evolution of northern temperate forest ecosystems. [ABSTRACT FROM AUTHOR]