Wildflowers of the United States

Slender Blue Flag, Slender Blue Iris, Coastal Iris - Iris prismatica

Genus Common Name: Iris

Native Status: Native

Monocot Perennial Herb

Iris prismatica - Slender Blue Flag, Slender Blue Iris, Coastal Iris. Iris is a genus of 225 to 280 species worldwide, about 30 to 35 growing wild in North America. Because of the large, showy flowers and easy growing nature, they are a popular garden plant. The American Iris Society shows 1425 different cultivated Irises.

Iris prismatica is a plant primarily native to the Atlantic Seaboard of the United States (let's include Pennsylvania in that description since Philadelphia has an ocean port via the Delaware River), along with disjunct populations in Tennessee and Alabama (and inland sites in seaboard states) which are known to oddly host otherwise coastal species. It is also reported to be found in the wild as likely introduced waif populations in West Virginia, and grows as in introduced species in Ontario and Nova Scotia, Canada. While the USDA map to the right doesn't show it in Alabama, there are vouchered specimens which were collected in Cherokee (1970, 1978) and Etowah (1995) Counties. It is rare throughout its range except for the relatively short range of New Jersey north through Massachusetts, and is legally protected in at least six states. It is a plant of brackish- and fresh-water swamps, bogs, and wet meadows.

Found in:
AL, CT, DE, GA, MA, MD, ME, NC, NH, NJ, NY, PA, RI, SC, TN, VA, VT, WV

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Distribution of Iris prismatica in the United States and Canada:

Map courtesy of The Biota of North America Program.
Map color key
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Site: AEDC, Coffee County, TN Date: 2017-May-24	Photographer: Gerald C Williamson Nikon D7000
The inflorescence of Iris prismatica consists of 1 to 3 flowers atop the stem which may be up to 3 feet tall. The pedicel arises out of a pale brown spathe.

Site: AEDC, Coffee County, TN Date: 2017-May-11	Photographer: Gerald C. Williamson Nikon D7000 Tamron SP 90MM f/2.8 AF Macro
Iris prismatica, as with all irises, has 3 petals and 3 sepals. They are a pale blue or violet/lavender (occasionally white.) The sepals have a white area, sometimes tinged yellow, and are dark-veined. The petals, held more erect, also may be dark-veined. What appears to be 3 more petals arching over the sepals are the typical Iris styles, colored similarly to the petals. The sepals are without crests.
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Site: AEDC, Coffee County, TN Date: 2017-May-11	Photographer: Gerald C Williamson Nikon D7000
Slender Blue Flag has both basal leaves as well as up to 4 cauline (stem) leaves. Both the stem and basal leaves stand erect, so they're difficult to differentiate. They are usually a few inches shorter than the flowering stems, and in their boggy habitat, difficult to differentiate from the surrounding foliage.
Click on the photo for a larger image
Site: AEDC, Coffee County, TN Date: 2017-May-11	Photographer: Gerald C Williamson Nikon D7000
Slender Blue Flag leaves are narrow - almost grass-like - usually less than 1/2 inch across.
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Iris prismatica initially published on USWildflowers.com 2017-06-22; Updated 2017-06-22

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All content except USDA Plants Database map Copyright Gerald C. Williamson 2024
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Code Update 20230302