General: Iris Family (Iridaceae). Western blue flag is a perennial herb, usually evergreen and growing from a creeping, tuberous rhizome. Rhizomes on blue flag are between 20-30 mm in diameter, quite large for a native iris. The leaves are long and linear with parallel venation, 3-9 mm wide, and sometimes purplish. Stems are 2-5 dm and sometimes branched. Blossoms of Iris missouriensis are pale lilac to whitish with lilac-purple veins.