Prickly Lettuce, a non-native, has been added to the USWildflowers database (09/30/2010.)  Scientific name is Lactuca serriola.  It’s also known by the common name China Lettuce.  Photo below was taken in downtown Chattanooga, TN on May 20, 2010.

Prickly Lettuce, China Lettuce - Lactuca serriola

Side note: This is the 100th species added to the USWildflowers database in 2010.