Iris tectorum alba (Japanese Roof Iris)
Iris tectorum "alba" is a beautiful white-blooming iris that I am particularly fond of. The story goes that this white Japanese Roof Iris was found growing on rooftops in Japan, as it was decreed at that time that land could only be used for food crops. I don't know about rooftops, but on terra firma this perennial grows to about 15 inches, and it likes its terra firma on the dry side. Iris tectorum "alba" has a lovely spreading habit, which makes it most attractive to look at and very agreeable when it comes to dividing. Sun. Zones 4-9.