Iris pseudacorus

 ( Pseudacorus ) 

Iris pseudacorus, the yellow flag, yellow iris, or water flag, is a species of flowering plant in the family Iridaceae. It is native plant to Europe, western Asia and northwest Africa. Its specific epithet pseudacorus means "false acorus", referring to the similarity of its leaves to those of Acorus calamus (sweet flag), as they have a prominently veined mid-rib and sword-like shape. However, the two plants are not closely related.

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Description This herbaceous flowering perennial plant grows to , or a rare tall, with erect leaves up to long and broad. The flowers are bright yellow, across, with the typical iris form. The fruit is a dry capsule long, containing numerous pale brown seeds.

I. pseudacorus grows best in very wet conditions, and is common in wetlands, where it tolerates submersion, low pH, and Anoxic waters soils. The plant spreads quickly, by both rhizome and water-dispersed seed. It fills a similar ecological niche to that of Typha and often grows with it, though usually in shallower water. While it is primarily an aquatic or marginal plant, the rhizomes can survive prolonged dry conditions.

Large I. pseudacorus stands in western Scotland form a very important feeding and breeding habitat for the endangered corncrake.

I. pseudacorus is one of two iris species native to the United Kingdom, the other being Iris foetidissima (stinking iris).

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Nectar production The plant was rated in second place for per day nectar production per flower in a UK plants survey conducted by the AgriLand project, which is supported by the UK Insect Pollinators Initiative. However, when number of flowers per floral unit, flower abundance, and phenology were taken into account, it dropped out of the top 10 for most nectar per unit cover per year, as did all plants that placed in the top ten, with the exception of common comfrey, Symphytum officinale.

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Cultivation It is widely planted in temperateness regions as an ornamental plant, with several selected for bog garden planting. The following cultivars have gained the Royal Horticultural Society's Award of Garden Merit:

• 'Roy Davidson'
• 'Variegata' (it has leaves that are edged with deep white stripes
  (2025). 9781856265034, Kyle Cathie Limited. ISBN 9781856265034
  )

Other cultivars known include Alba (with pale cream flowers) and Golden Fleece (with dark yellow flowers).

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Invasive species In some regions (including the US and South Africa) where it is not native, it has escaped from cultivation to establish itself as an invasive species aquatic plant which can create dense, monotypic stands, outcompeting other plants in the ecosystem. Where it is invasive, it is tough to remove on a large scale. Even ploughing the rhizomes is often ineffective. It has been banned in some areas but is still widely sold in others for use in gardens.

Iris pseudacorus is reported as invasive in Connecticut, Delaware, Maryland, New Hampshire, New Jersey, North Carolina, Oregon, Tennessee, Virginia, Vermont, Washington, Wisconsin, and West Virginia.

+US Spread !State/Province !First Observed
Illinois	2009
Indiana	1982
Michigan	1932
Minnesota	2008
NY	1882
Ohio	2013
Pennsylvania	1954
Vermont	1909
Wisconsin	2005

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Relationship to fleur-de-lis According to Pierre Augustin Boissier de Sauvages, an 18th-century French Natural history and lexicography, the name fleur-de-lis applied to the Heraldry symbol may be related to Iris pseudacorus rather than to a lily, based on the shape and yellow colour of the flower.

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Toxicity and uses The plant's roots and leaves are poisonous.

(2025). 9781402767159, Sterling. ISBN 9781402767159

This plant has been used as a form of water treatment since it can take up macronutrients (such as nitrogen and phosphorus) through its roots, and is featured in many AS Level Biology practicals as its ability to grow in low pH levels makes it a useful indicator.

It can also Halophyte in the water.

==Gallery==

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See also

• Flag of the Brussels-Capital Region
• Fleur-de-lis
• Iris sawfly

• Flora Europaea: Iris pseudacorus

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External links

• Plants for a Future: Iris pseudacorus

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