First, let's dispel the confusion that surrounds this group: Once they were known as Kaempferi Irises, today many call them "The Butterfly Irises", but the correct common name is simply "Japanese Iris." In luscious colors of purple, pink, and endless bicolors, they have been cultivated in Japan for over 500 years, and were once restricted to enjoyment by royalty only. Though many think they are, they are not water dwellers. They require about the same conditions as ferns, astilbes or impatiens—just moist ground, which most all gardeners can easily provide.
As you can see by the photos, these iris blooms are quite different from the tall "stand-up" flowers of the big Bearded Irises. With Japanese Irises, both sets of petals are more flat, forming a simpler, flatter--and many think more beautiful--flower. Japanese Irises form large lavish hardy clumps and are highly decorative. They're also great for cutting.
Source: American Meadows