In Greek Mythology, Iris is the goddess of the rainbow and messenger to the gods. (In Greek iris translates to "the rainbow," and eiris, "messenger.") She was a symbol of the connection between the heavens and the earth, serving as a mediatrix between gods and mortals. The goddess is a common figure in Greek poetry and myth, most notably in Homer’s Iliad: “swift wind-footed Iris” (Iliad. xxiii. 168).
Not surprisingly then, Greenaway writes that Irises mean “message.” I wonder about the connection of a fleet-footed messenger and the flower itself. Irises bloom late May, early June (here in Chicago at least), they last a while in the garden, but as cut flowers, they are very short lived. Perhaps there is a connection between the ephemerality of a rainbow and the fleeting nature of this flower. Or perhaps it's the variety of color and it's arched petals that invite the comparison.
I didn't know this before researching, but I found it very interesting that the Irises are the flower depicted in the fleur de lis. I’m nerding out a little about it --don’t worry, I’ll spare you-- but if you’re interested, go to the Iris Wikipedia page and read about the origin of the fleur de lis.
That's all for now.