|Rhizomatous irises have rhizomes as rootstocks, close to or on the surface, or just below ground-level, which produce linear to sword-shaped leaves, nearly always in basal fans, and simple or branched flower stems. The flowers have 3 upright petals, called standards, and 3 large, pendent or spreading petals, called falls.
Siberian irises lack the "beard" of colored hairs at the base of each fall that other iris groups have. Siberian irises bloom from midspring to early summer. Best planted from midsummer to early fall; apply shallow mulch in the spring. 'Shirley Pope' bears deep purple flowers with white spots on the falls, almost a black and white look.