Terrestrial Invasives

Iris pseudacorus

Iris pseudacorusYellow flag iris

Common Name 
Yellow flag iris
Legal Status 
Emerging Weed

Yellow flag iris forms dense growth along riverbanks and the fringes of ponds, competing with indigenous species and altering water flow. It is a perennial moisture-loving plant with yellow flowers and long, strap-like leaves. It reaches a height of 100-150cm.

Leaves: Long, strap-like leaves, green to bluish-green and erect, with the upper part bending over. Leaves 1m long and 30mm wide.

Flowers: Large yellow flowers with three narrow and three broad lobes 70mm long and 40mm wide.

Fruit/seeds: Glossy green three-angled capsules which are 40-80mm long.

Yellow flag iris can grow up to 1.5m tall
Yellow flag iris flower
Yellow flag iris flower
Where does this species come from? 
Europe, Western Asia, North Africa
Why is it a problem? 
It can easily invade similar aquatic ecosystems when it is introduced by forming dense growth, which can reduce water movement and displace other submerged aquatic plants. This plant is poisonous to livestock due to its toxic properties.
Means of reproduction? 
Yellow flag spreads by seeds and rhizomes. Up to several hundred flowering plants may be connected through rhizomes. Rhizome fragments can form new plants if they break off and drift to suitable habitat. Although aquatic, rhizomes can survive long periods of drought, and seed dispersal occurs by flowing water.