A fossil-calibrated relaxed clock for Ephedra indicates an Oligocene age for the divergence of Asian and New World clades and Miocene dispersal into South America
Stefanie M. ICKERT-BOND, Catarina RYDIN, Susanne S. RENNER
J Syst Evol . 2009, (5): 444 -456 .  DOI: 10.1111/j.1759-6831.2009.00053.x