Japanese Iris.

These irises crave dampness. 

I try to provide it for them, but it is a chore.  Lovely along a stream bank or pond.  I do not know what to say about this plant that the photo cannot top.  It is actually much more beautiful in person, if that is possible.  Much like Siberian irises in appearance of the plant, but slightly larger and sturdier leaves.  The color variations are legion.  I just love this velvety royal blue/purple.  The white edges look like frost.