Kimberly J. Smith

Kimberly J. Smith

Monocotyledoneae (Monocots)
Iridaceae (Iris Family)
State Protection
Federal Protection
Not Listed
State Conservation Status Rank
Global Conservation Status Rank


Did you know?

The roots and rhizomes contain the glycoside iridin that is somewhat poisonous and a skin irritant (Lady Bird Johnson Wildflower Center 2010). That is why it sometimes has the common name poison flagroot.

State Ranking Justification

There are 15 existing populations and about half of these have 100 plants are more. Three populations have over 1000 plants. Forty-one populations were documented from the late 1800s through the 1960s but about half of these no longer exist because their habitat has been destroyed. About 20 populations need to be checked to determine if they still exist.

Short-term Trends

Most populations have been visited more than once and they seem stable.

Long-term Trends

Populations have declined by over one half in the last 100 years as many wetlands in the New York City area and Western Long Island have been destroyed. If the remaining wetlands can be preserved and managed well then populations should remain viable into the foreseeable future.

Conservation and Management


Populations are threatened by off-road vehicles, trampling, mosquito ditches, fragmentation and hydrological alteration from a road crossing and by the expansion of stands of Phragmites.

Conservation Strategies and Management Practices

Wetlands need to have sufficient natural buffers established around them to preserve hydrology and invasive species, especially Phragmites, need to be controlled.



In New York Slender Blue Flag is known from a variety of open, wet, coastal habitats. It has been collected in sea level fens and the edges of salt marshes and brackish meadows, as well as from diverse disturbed habitats such as burned or scraped old fields, ditches, and roadside swales (New York Natural Heritage Program 2010). Swampy, peaty soil (FNA 2002). Moist meadows and sandy or gravelly shores (Rhoads and Block 2000). Marshes, swamps, and damp meadows (Gleason and Cronquist 1991).

Associated Ecological Communities

  • Brackish interdunal swales* (guide)
  • Brackish meadow (guide)
  • Coastal plain pond* (guide)
  • Coastal plain pond shore (guide)
  • Ditch/artificial intermittent stream
  • High salt marsh (guide)
  • Maritime shrubland (guide)
  • Mowed roadside/pathway
  • Rich graminoid fen* (guide)
  • Sea level fen (guide)
  • Successional old field*

Associated Species

  • Amelanchier canadensis
  • Artemisia vulgaris (mugwort)
  • Asclepias incarnata
  • Baccharis halimifolia (groundsel-tree)
  • Carex lurida (sallow sedge)
  • Cirsium horridulum
  • Cladium mariscoides (twig-rush)
  • Clethra alnifolia (coastal sweet-pepperbush)
  • Comarum palustre (marsh-cinquefoil)
  • Drosera rotundifolia (round-leaved sundew)
  • Equisetum arvense (field horsetail, common horsetail)
  • Euthamia caroliniana (slender flat-topped-goldenrod)
  • Fimbristylis autumnalis (autumn fimbry)
  • Hibiscus moscheutos ssp. moscheutos (swamp rose-mallow)
  • Ilex verticillata (common winterberry)
  • Impatiens capensis (spotted jewelweed, spotted touch-me-not)
  • Juncus canadensis (Canada rush)
  • Juncus effusus
  • Juncus gerardii
  • Juniperus virginiana
  • Lobelia nuttallii (Nuttall's lobelia)
  • Lonicera morrowii (Morrow's honeysuckle)
  • Lycopus americanus (American bugleweed, American water-horehound)
  • Lythrum salicaria (purple loosestrife)
  • Myrica pensylvanica
  • Nyssa sylvatica (black-gum, sour-gum)
  • Oenothera perennis (small sun-drops)
  • Onoclea sensibilis (sensitive fern)
  • Osmunda cinnamomea
  • Osmunda regalis
  • Panicum virgatum (switch grass)
  • Photinia melanocarpa
  • Phragmites australis (old world reed grass, old world phragmites)
  • Pinus rigida (pitch pine)
  • Pluchea odorata (salt marsh-fleabane)
  • Potentilla simplex (old-field cinquefoil)
  • Prunus serotina
  • Pycnanthemum virginianum (Virginia mountain-mint)
  • Quercus palustris (pin oak)
  • Rhamnus cathartica (European buckthorn)
  • Rhynchospora fusca (sooty beak sedge)
  • Rosa carolina
  • Rosa multiflora (multiflora rose)
  • Schizaea pusilla (curly-grass fern, curly-grass)
  • Schoenoplectus americanus (chair-maker's bulrush)
  • Schoenoplectus pungens
  • Scirpus cyperinus (common wool-grass)
  • Scutellaria galericulata (marsh skull-cap)
  • Smilax rotundifolia (common greenbrier)
  • Solanum dulcamara (bitter-sweet nightshade)
  • Spartina patens (salt-meadow cord grass)
  • Sphagnum
  • Spiraea tomentosa (steeplebush)
  • Symplocarpus foetidus (skunk-cabbage)
  • Teucrium canadense (American germander)
  • Thelypteris palustris
  • Toxicodendron radicans
  • Triadenum virginicum
  • Tripsacum dactyloides
  • Typha angustifolia (narrow-leaved cat-tail)
  • Vaccinium corymbosum (highbush blueberry)
  • Vernonia noveboracensis (New York ironweed)
  • Viburnum dentatum var. lucidum (smooth arrowwood)
  • Viburnum dentatum var. venosum (southern arrowwood)


New York State Distribution

This small herb is currently known from the Bronx, Staten Island and Suffolk County on Long Island. It was historically known north of New York City to Rockland County with a report as far north as Dutchess County. It was also reported from the salt marshes near Syracuse which were subsequently destroyed by industrialization.

Global Distribution

This wetland herb is primarily from the Atlantic coastal plain from Nova Scotia and Maine south to Georgia. There are scattered inland populations in Pennsylvania south to Georgia, Alabama, and Tennessee.

Best Places to See

  • Pelham Bay Park
  • Napeague State Park (Suffolk County)

Identification Comments

General Description

Slender Blue Flag is a perennial herb species growing from 30 to 80 centimeters tall from cordlike roots. The leaves are grasslike, erect, and 2 to 5 millimeters wide, with a central rib. The infloresence of 1 to 3 flowers is held on an erect, simple or slightly branched stem. The flowers are large (4-5 centimeters wide), the 3 sepals pale violet with yellow patches near the base and 3 lavender petals. The sepals also have small (5-7 millimeter), toothed, purple appendages called crests emerging from their bases opposite the yellow patches. The fruits are 3-sided capsules 3 to 4 centimeters long, containing one row of seeds per locule (FNA 2002).

Best Life Stage for Proper Identification

Iris prismatica may be identified in vegetative form, but more easily so when in flower or fruit.

Similar Species

The most common tall, violet-flowered Iris in New York, Iris versicolor, has leaves one to three centimeters wide. The only other tall, violet flowered Iris i with narrow leaves n New York is I. sibirica. It differs from Iris primatica by having hollow stems, flowers with white patches at the base of the sepals, and fruits with two rows of seeds per locule (FNA 2002).

Best Time to See

Iris prismatica flowers from June through July, and remnant fruit stalks may persist year round.

  • Vegetative
  • Flowering
  • Fruiting

The time of year you would expect to find Slender Blue Flag vegetative, flowering, and fruiting in New York.

Slender Blue Flag Images


Slender Blue Flag
Iris prismatica Pursh ex Ker-Gawl.

  • Kingdom Plantae
    • Phylum Anthophyta
      • Class Monocotyledoneae (Monocots)
        • Order Liliales
          • Family Iridaceae (Iris Family)

Additional Common Names

  • Coastal Iris

Additional Resources

Best Identification Reference

Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.

Other References

Clemants, Steven and Carol Gracie. 2006. Wildflowers in the Field and Forest. A Field Guide to the Northeastern United States. Oxford University Press, New York, NY. 445 pp.

Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.

Flora of North America Editorial Committee. 2002. Flora of North America, North of Mexico. Volume 26. Magnoliophyta: Liliidae: Liliales and Orchidales. Oxford University Press, New York. 723 pp.

Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.

New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.

New York Natural Heritage Program. 2019. New York Natural Heritage Program Databases. Albany, NY.

Newcomb, Lawrence. 1977. Newcomb's Wildflower Guide: An Ingenious New Key System for Quick, Positive Field Identification of the Wildflowers, Flowering Shrubs, and Vines of Northeastern and North-Central North America. Little, Brown and Company. Boston.

Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research University of South Florida]. New York Flora Association, Albany, New York


About This Guide

Information for this guide was last updated on: November 17, 2011

Please cite this page as:
New York Natural Heritage Program. 2019. Online Conservation Guide for Iris prismatica. Available from: Accessed March 20, 2019.

Back to top