Iris pseudacorus
Iris pseudacorus iris des marais.jpg
Scientific classification edit
Kingdom: Plantae
Clade: Tracheophytes
Clade: Angiosperms
Clade: Monocots
Order: Asparagales
Family: Iridaceae
Genus: Iris
Subgenus: Iris subg. Limniris
Section: Iris sect. Limniris
Series: Iris ser. Laevigatae
I. pseudacorus
Binomial name
Iris pseudacorus
List of synonyms
  • Iris acoriformis Boreau
  • Iris acoroides Spach
  • Iris bastardii Boreau
  • Iris curtopetala F. Delaroche
  • Iris curtopetala F. Delaroche ex Redoute
  • Iris flava Tornab.
  • Iris lutea Lam.
  • Iris pallidior Hill
  • Iris paludosa Pers.
  • Iris pseudacorus var. acoriformis (Boreau) Nyman
  • Iris pseudacorus subsp. acoriformis (Boreau) K.Richt
  • Iris pseudacorus var. acoroides (Spach) Baker
  • Iris pseudacorus var. bastardii (Boreau) Nyman
  • Iris pseudacorus subsp. bastardii (Boreau) K.Richt.
  • Iris pseudacorus var. citrina Hook.
  • Iris pseudacorus f. longiacuminata Prodán
  • Iris pseudacorus f. nyaradyana Prodán
  • Iris pseudacorus var. ochroleuca Peterm.
  • Iris pseudacorus f. submersa Glück
  • Iris sativa Mill.
  • Limnirion pseudacorus (L.) Opiz
  • Limniris pseudacorus (L.) Fuss
  • Moraea candolleana Spreng.
  • Pseudo-iris palustris Medik.
  • Vieusseuxia iridioides F.Delaroche
  • Xiphion acoroides (Spach) Alef.
  • Xiphion pseudacorus (L.) Schrank
  • Xyridion acoroideum (Spach) Klatt
  • Xyridion pseudacorus (L.) Klatt

Iris pseudacorus, the yellow flag, yellow iris, or water flag, is a species of flowering plant in the family Iridaceae. It is native 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.



This herbaceous flowering perennial plant grows to 100–150 cm (39–59 in), or a rare 2 m (6 ft 7 in) tall, with erect leaves up to 90 cm (35 in) long and 3 cm (1.2 in) broad. The flowers are bright yellow, 7–10 cm (2.8–3.9 in) across, with the typical iris form. The fruit is a dry capsule 4–7 cm (1.6–2.8 in) 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 soils. The plant spreads quickly, by both rhizome and water-dispersed seed. It fills a similar 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).

Both the petals and stem are toxic to animals and plants.[citation needed]

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.[2]


It is widely planted in temperate regions as an ornamental plant,[3] with several cultivars selected for bog garden planting. The following cultivars have gained the Royal Horticultural Society's Award of Garden Merit:[4]

  • 'Roy Davidson' [5]
  • 'Variegata' [6] (it has leaves that are edged with deep white stripes [7])

Other cultivars known include; Alba (with pale cream flowers) and Golden Fleece (with dark yellow flowers).[7]

It used to grow in the ditch of the fortified city of Mdina, on the island of Malta, where water was readily available, but since the renovation of the ditch it has since vanished from the area.[8]

Invasive species

In some regions (including the USA and South Africa)[9] where it is not native, it has escaped from cultivation to establish itself as an invasive 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.[10]

Toxicity and uses

The plant's roots and leaves are poisonous.[11]

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,[12] and is featured in many AS Level Biology practicals as its ability to grow in low pH levels makes it a useful indicator.[citation needed]

It can also withstand high salinity levels in the water.[13]


See also


  1. ^ "Iris pseudacorus L. is an accepted name". (The Plant List). 23 March 2013. Retrieved 14 April 2015.
  2. ^ "Which flowers are the best source of nectar?". Conservation Grade. 2014-10-15. Retrieved 2017-10-18.
  3. ^ "RHS Plant Selector - Iris pseudacorus". Retrieved 24 June 2013.
  4. ^ "AGM Plants - Ornamental" (PDF). Royal Horticultural Society. July 2017. p. 53. Retrieved 13 March 2018.
  5. ^ "Roy Davidson". RHS. Retrieved 25 September 2020.
  6. ^ "RHS Plant Selector - Iris pseudacorus 'Variegata'". Retrieved 7 September 2020.
  7. ^ a b Spencer-Jones, Rae; Cuttle, Sarah (2005). Wild Flowers of Britain and Ireland. London: Kyle Cathie Limited. p. 88. ISBN 9781856265034.
  8. ^ Schembri, Patrick J.; Baldacchino, Alfred E. (2011). Ilma, Blat u Hajja: Is-Sisien tal-Ambjent Naturali Malti (in Maltese). p. 81. ISBN 978-99909-44-48-8.
  9. ^ Mostert, Esther; Weaver, Kim (eds.). "Centre for Biological Control Annual Report 2019" (PDF). Centre for Biological Control, Rhodes University.
  10. ^ McIntosh, Jamie (21 June 2021). "9 Top Types of Iris for the Flower Garden". The Spruce. Retrieved 29 July 2021.
  11. ^ Elias, Thomas S.; Dykeman, Peter A. (2009) [1982]. Edible Wild Plants: A North American Field Guide to Over 200 Natural Foods. New York: Sterling. p. 261. ISBN 978-1-4027-6715-9. OCLC 244766414.
  12. ^ Mohseni-Bandpei, A. (2010). "Nitrogen and phosphorus removal from wastewater by subsurface wetlands planted with Iris pseudacorus". Ecological Engineering. 36 (6): 777–782. doi:10.1016/j.ecoleng.2010.02.002.
  13. ^ Zhao, Huilin; Wang, Fen; Ji, Min (2015). "Brackish Eutrophic Water Treatment by Iris pseudacorus L.-Planted Microcosms: Physiological Responses of Iris pseudacorus L. to Salinity". International Journal of Phytoremediation. 17 (9): 814–821. doi:10.1080/15226514.2014.981240. PMID 25529785. S2CID 30542002.

External links