Rhizomes compact, freely branching, forming dense clumps, 0.9-1.2 cm diam., covered with remnants of old leaves. Stems simple or 1-3-branched, hollow, 6-12 dm. Leaves dying back in winter, blade dark green, often tinged pink at base, 4-8 dm × 0.4-0.6 cm. Inflorescence units 3-5-flowered, lateral units 2-3-flowered; spathes brown, to 4 cm, narrow, papery, apex acute. Flowers: perianth light to dark blue-violet to white; floral tube with indistinct ribs, circular, ca. 1 cm; sepals flaring or curving downward apically, widely orbiculate, 5-7 × 2-2.5 cm, base abruptly attenuate into claw with two narrow flanges basally, signal white, semicircular, with dark violet veins basally; petals erect, narrowly elliptic-obovate, 4.5-5.5 × 1.5-1.8 cm; ovary roundly triangular, spindle-shaped, 1.5-2 cm; style pale blue, bluntly keeled, 4-5 cm, crests overlapping, triangular, margins crenate; stigmas tonguelike projections, triangular; pedicel 1-15 cm, unequal, later flowers in each spathe with longer pedicel. Capsules roundly triangular with low ridges at angles, 3-4.5 × 1-1.3 cm, smooth, apex with extremely short tip, opening only in upper 1/4-1/3 of capsule. Seeds in 2 rows per locule, dark brown, D-shaped, flattened, 5 × 3 mm, slightly roughened by small, rounded protuberances. 2n = 28.

Flowering May--Jul. Widely cultivated, found along roadsides; introduced; Ont.; Calif., Conn., Maine, Mass., N.Y., Pa., Vt.; expected elsewhere; Eurasia.

Many forms of Iris sibirica have been cultivated widely across North America, where it is quite hardy and persistent.