There's also the Southern Blue Flag, iris virginica, which is another American native. It does well all over the South.
I agree, the I. pseudacorus is a terrible pest. The pond here at our house had them when we moved in, and what a terrible job to remove them. The rhizomes were the size of my wrist! Luckily mine never bloomed unless I let the pond water level drop a lot, so I never had them make seed and get away on me.
My pond now has Blue Flags and Louisiana iris 'Black Gamecock' which is the most gorgeous deep purple ever, and blooms even if the water level doesn't drop.
