identification

I hope some one can help me id this iris, I don't have a camera, and if I did I wouldn't know how to "post" it anyway. I found this iris shortly after I bought my property 9 years ago. I think it is a louisiana from reading the descriptions on this website. It is white with yellow at the base of the lowest set of petals or "falls" I don't know the difference, the uppermost petals stand up, the other two sets curve slightly down. It is approx 11/2 to 2 inches across, the foliage is wider than two irises I know to be siberian and about 2 or 3 feet tall. It is very vigorous, when I found it (in an area around an old tree that I had always mowed before) it was 3 little blades. It is now every where on a 31/2 acre property, I have divided it so many times. It grows equally well at the edge of my pond, in my borders, on a sunny bank beside my driveway, and at the edge of the woods in half sun. I would grow this plant if I found out it was a weed, I love it, but I was hoping someone might be able to give me a name.