Iris prismatica isa perennial monocotyledon, colonial from a slender, creeping rhizome at surface of soil and slightly buried stolons 0.2-0.5 cm diameter, stolon tips sprouting new plants, which give rise to flowering stems the following season.
Leaves mostly basal, in tufts from stolon tips, linear 50-70 cm long, 0.3-0.7 cm wide, bases reddish, 1-4 along flowering stem.
Flowers blue-violet with white and green variegations at base, radially symmetrical, 6-8 cm wide, petals 3, 3.5-4.5 cm long, 0.7-1.5 cm wide, erect, sepals 3, 1.3-2 cm wide, yellowish at base, pendant, larger than petals, both narrowed at base, anthers bluish; inflorescence at top of stem with 1-2 branches each with 1-3 flowers, flowering stems solitary, 20-75 cm tall; blooms June-July.
Fruit dry, an oblong 3-parted capsule1.5-4.5 cm long, 1.2–1.4 cm wide, sharply 3-angled to nearly winged, splitting open to release thick, angular seeds during winter, probably water dispersed.
Wetland status: OBL.
Frequency in NYC: Infrequent (NYS Rare, S2).
Habitat: Open, or part shaded, undisturbed marshes and swamp forests, salt marsh edges, mostly coastal. Planted at wetland mitigation site in Graniteville S.I. and at other wetland restoration and mitigation sites.
Notes: Listed as endangered in several other northeastern states (USDA, NRCS 2006).