A Catter called Taconicus has located original sheet music for Wildwood Flower at UCLA. The mystery flower is the aronatis. Or maybe aronatus.

Since I can't find a record of any such flower, I changed the words to "pale, blooming iris with falls of bright blue." The Long petals of an iris which drop down toward the ground are called falls, and they are usually more intense in color (hence brighter) than the rest of the flower.