From the "Garden Saints" series.

The flower is named after the elemental Greek goddess Iris: messenger of the gods, enforcer of oaths, and advocate for fairness. Oaths are sealed with water from the underworld River Styx, which she carries with her, employing swift and unorthodox transportation: rainbows, wind, wings, and beasts. She also carries a herald's staff, and (as granddaughter of Oceanus) she consorts with storms, rivers, and waterfalls. Her name is used for "rainbow" in Greek and many other languages, and it is the origin of "iridescence" in English. Her strong association with color led to the naming of Iris flowers, the colorful iris in the human eye, and the analogous iris of a camera.