Phylogeny and biogeography of Juglans (Juglandaceae) based on matK and ITSsequence data

We investigated phylogenetic and biogeographic relationships within Juglans (walnuts), a Tertiary disjunct genus, using 15 species of Juglans and rela ted (Juglandaceae) outgroups. The relationships were analyzed using nucleot ide sequences of the chloroplast gene matK and its flanking spacers and of the internal transcribed spacers (ITS) and 5.8S gene of the nuclear ribosom al DNA. The DNA sequences provided 246 informative characters for parsimony analysis. ITS data supported as monophyletic groups the four generic secti ons, Cardiocaryon, Dioscaryon, Rhysocaryon, and Trachycaryon. Within Rhysoc aryon, the temperate black walnuts and the tropical black walnuts were supp orted as monophyletic groups. When the two data sets were combined. J. cine rae was nested within Cardiocaryon. Combined analysis with published nuclea r DNA restriction site data placed J. cinerea in a monophyletic group with Cardiocaryon. These analyses consistently supported Juglans as a monophylet ic group and as the sister group to the genus Pterocarya. The results of th is work are consistent with the known geological history of Juglans. The fo ssil record suggests: that the butternuts had evolved by the early Oligocen e in North America. The presence of butternuts in Eurasia could be the resu lt of migration from North America to Eurasia during the warming trend of t he mid Oligocene.