Dwarf Crested Iris (Iris cristata) is a native Iris that thrives in part shade. It is a ‘streambank’ plant that tolerates drought and flooding- in fact it does a great job controlling erosion at the edge of a slope.

3rd picture is ‘Tennessee White’, a white cultivar planted near some ‘May Breeze’ Woodland Phlox (Phlox divericata), another native at peak bloom right now.

More about Iris cristata here: http://www.wildflower.org/plants/result.php?id_plant=IRCR