My take on it is, if a "stranger" shows up in your clump of iris.....we'll say, it has white standards, while the clump is of an "all purple variety......and, after close inspection, you find it wasn't from a "dropped seed", but actually from a "rhizome connected to" the original......and, after removal, and replanting, it continues to have white standards (which would show that it ISN'T a Chimera caused by weather or chemical contact), it would be a "sport"
