Paul Manos and John McVay have joined with Andrew Hipp at the Morton Arboretum and other colleagues from the University of Minnesota and the Universidad Nacional Autónoma de México to publish "Sympatric parallel diversification of major oak clades in the Americas and the origins of Mexican species diversity New Phytologist, 18 September 2017, 10.1111/nph.14773).  The paper crunched large amounts of data drawn from 300 samples, comprising 146 species of oak.  Next-generation sequencing techniques enabled the researchers to construct a phylogenetic tree of the genus Quercus going back 45 million years.  They concluded that the ancestor of North American oaks arose near the Arctic Circle, and gradually spread southward as the climate became more temperate.  A variety of ecological niches in Mexico encouraged the oaks to evolve a great number of different species there.  

The news was startling enough that Science magazine published a news story about it (http://www.sciencemag.org/news/2017/09/one-world-s-most-popular-trees-a…).  Congratulations to Paul and John for unlocking a long-standing mystery!