David, One expression for this that I recall is Rassenkreis, a breeding or racial circle or arc. I think I have seen "cline" applied to the sort of variational gradient you describe. We still someone who knows for sure to enlighten us! Jim Shields At 07:04 PM 12/20/2007 -0800, David wrote: >There is a botanical word I'm looking for it's something like gradient, >but I don't think that's the word. It is used when referring to a species >with a broad distribution which has one form at one end of its >distribution and a very different form at the other end. The two extreme >forms are sometimes considered separate species. But when the >distribution is continuous and every intermediate form is found and there >is no bar to interbreeding, this special word is used, and the population >is considered a single species with disparate extreme forms > ************************************************* Jim Shields USDA Zone 5 Shields Gardens, Ltd. P.O. Box 92 WWW: http://www.shieldsgardens.com/ Westfield, Indiana 46074, USA Tel. ++1-317-867-3344 or toll-free 1-866-449-3344 in USA