Hello: I think the hisrotical geology and climate also affected it. http://www.scotese.com/paleocli.htm http://en.wikipedia.org/wiki/Floristic_province/ The high lands in the tropical america may help some species to move. the border is a filter. And why not is the flora of tropical america stops at Mexco -USA border? Because we are in a warming Interglacial. Fierycloud Taiwan. ----- Original Message ----- From: Alani Davis <alanidae@gmail.com> To: Pacific Bulb Society <pbs@lists.ibiblio.org> Date: Thu, 25 Mar 2010 17:22:23 -0400 Subject: [pbs] border debates > "The Flora of North America seems to stop at the Mexico-USA border. > Where are all our experts when you need one?" > > > Which part of the North American flora stops at the Mexican United States? > There are many genera that bridge that artificial line. Oaks, pines, maples, > magnolias, Mahonia, all occur on both sides and in some cases the same > species and there are plenty of others that don't range widely in the > northern United States but occur throughout the southeast and southwest U.S. > If I have the correct greatest diversity of Pinus and Quercus species in the > world is found in Mexico. Another interesting twist, the cycad genus, > *Ceratozamia > *represented by several species in Mexico, Guatemala, and Belize is > represent in fossil form from Alaska. Seems to me there is a fair amount of > moving around. > > Alani Davis > > > > -- > Alani > _______________________________________________ > pbs mailing list > pbs@lists.ibiblio.org > http://pacificbulbsociety.org/list.php > http://pacificbulbsociety.org/pbswiki/ >