More slender in every way than Iris versicolor Linnaeus, with a tuberous-thickened rootstock; stem 1 to 3 feet tall, bearing two or three very narrow, almost grasslike leaves usually less than one-fourth of an inch wide; flowers one or two at summit of each stem, blue, veined with yellow on slender pedicels; outer perianth segments one-half to 2 inches long, smooth and devoid of a crest, the inner segments smaller and narrower; the perianth tube about one-fourth of an inch long above the ovary. Fruit a narrowly oblong capsule, acute at each end and sharply three-angled, 1 to 1 ½ inches long.
Memoir 15 N. Y. State Museum
Narrow Blue Flag; Poison Flagroot - Iris prismatica