Iris pseudacorus, the yellow flag, yellow iris, or water flag, is a speciesofflowering plant in the familyIridaceae. It is native to Europe, western Asia and northwest Africa. Its specific epithetpseudacorus 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).
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]
'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 after the renovation of the ditch it has since vanished from the area.[8]
In some regions (including the US and South Africa)[9] where it is not native, it has escaped from cultivation to establish itself as an invasiveaquatic 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]
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,[14] 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.[15]
^Mohseni-Bandpei, A. (2010). "Nitrogen and phosphorus removal from wastewater by subsurface wetlands planted with Iris pseudacorus". Ecological Engineering. 36 (6): 777–782. Bibcode:2010EcEng..36..777Y. doi:10.1016/j.ecoleng.2010.02.002.
^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. Bibcode:2015IJPhy..17..814Z. doi:10.1080/15226514.2014.981240. PMID25529785. S2CID30542002.
