Sp. Pl. 1: 39. 1753.
Rhizomes many-branched, forming dense clumps, 2–4 cm diam., usually covered with remnants of old leaves; roots fleshy. Stems rather weak, often falling over after flowering, solid, usually 1-branched, 5–10 dm. Leaves: basal erect or often flexible, blade gray-green to bright green, buff to purplish basally, with several prominent ribs in mature leaves, linear-ensiform, 6–8 dm × 2.5–3 cm, apex acute. Inflorescence units 2–3-flowered, branch units 1–2-flowered; spathes compact, often with brown striations, ridged, unequal, outer 3–8 cm, inner 8–14 cm, firm, herbaceous. Flowers: perianth lavender to violet, rarely white; floral tube constricted above ovary, 1–2 cm; sepals spreading and arched, pale blue to purple with darker blue or purple lines, obovate to oval, 4–8.4 × 1.6–4 cm, base abruptly attenuate, claw green in median, bordered by yellow ground with blue or purple lines, yellow extending onto base of limb as finely pubescent signal patch; petals oblong-lanceolate to oblong-spatulate, 3–7 × 1–3 cm, claw greenish yellow with blue or purplish lines, apex often emarginate; ovary trigonal, 1.3–3.8 cm; style inwardly auriculate at convergences, 3–4.5 cm, crests reflexed, 0.7–2 cm; stigmas unlobed, with prominent triangular tongues, margins entire; pedicel 2.5–8 cm. Capsules ovoid, ellipsoid, or long-cylindric, trigonal or polygonal in cross section, 3–6 × 1–2 cm. Seeds in 2 rows per locule, pale brown, usually D-shaped, 5–8 mm, pitted, corky. 2n = 70, 72.
Phenology: Flowering May–Jun.
Habitat: Wetlands, margins of lakes and streams
Ont., Que., Ala., Ark., D.C., Fla., Ga., Ill., Ind., Iowa, Kans., Ky., La., Md., Mich., Minn., Miss., Mo., Nebr., N.Y., N.C., Ohio, Okla., Pa., S.C., Tenn., Tex., Va., W.Va., Wis.
Plants of Iris virginica from the southeastern and south-central states having stems 2–3-branched and seldom falling to the ground after flowering, and with capsules long-cylindric have been recognized as var. shrevei.