T.E.R:R.A.I.N - Taranaki Educational Resource: Research, Analysis and Information Network


Iris pseudacorus (Yellow flag iris)

Kingdom: Plantae
(unranked): Angiosperms
(unranked): Monocots
Order: Asparagales
Family: Iridaceae
Subfamily: Iridoideae
Tribe: Irideae
Genus: Iris
Subgenus: Limniris
Species: I. pseudacorus
Binomial name: Iris pseudacorus
Common name: Yellow flag iris, Yellow flag, Water flag.

Iris pseudacorus is native to Europe, western Asia and northwest Africa. It is an is a leafy wetland-terrestrial iris, that grows to >150 centimetres tall, with erect leaves that are up to 90 centimetres long and 20 to 30 mm wide and has a distinctive mid rib. The flowers are bright yellow, 120 mm across, with the typical iris form and are present during September to December. The fruit is a dry capsule 4–7 centimetres long, containing numerous smooth, pale brown seeds which float on water. 
Yellow flag iris grows best in very wet conditions, and is often common in wetlands, where it tolerates submersion, low pH, and anoxic soils. The plant spreads quickly, by both rhizome and water-dispersed seed. While it is primarily an aquatic plant, the rhizomes can survive prolonged dry conditions.
The plant will remain green during the winter where the weather is mild, but leaves will die back during periods of prolonged drought or below-freezing temperatures

Introduced to New Zealand as an ornamental garden plant, it has now escaped from cultivation to establish itself as an invasive aquatic plant throughout New Zealand. It grows in the margins of still, fresh or slightly salty water such as rivers, swamps, salt marshes and pond edges. It can create dense, monotypic stands, out competing other plants in the ecosystem. It can also invade and displace low lying pasture and is toxic to livestock. Where it is invasive, it is tough to remove on a large scale. Even ploughing the rhizomes is often ineffective. The poisonous seeds may have an impact on birdlife.