Skip to main content

Species - Yellow iris / Yellow flag

Status

Widespread

Yellow iris / Yellow flag (Iris pseudoacorus)

A rhizomous, herbaceous, perennial plant that can be found throughout the UK and much of the rest of Europe, western Asia and northwest Africa.  In western Scotland, the Yellow Iris forms an important feeding and breeding habitat for the Corncrake, a species whose numbers have been in decline in the UK. Often planted as an ornamental plant, with several cultivars selected for bog garden planting.

Common in wet conditions, this aquatic or semi-aquatic plant can tolerate submersion, low pH, and anoxic soils. Grows typically 1 to 1.5 m tall (or rarely 2 m), with erect leaves up to 90 cm long and three cm broad. Its specific name, meaning 'false acorus', refers to the similarity of its leaves to those of Acorus calamus, which has a prominently veined mid-rib and sword-like shape.   In open, unshaded conditions, the Yellow Iris will flower and set seed, producing bright yellow flowers from July to August, seven to ten centimetres across.

Flowers are usually pollinated by long-tongued insects such as bumble bees. The yellow petals provide a platform for insects to land on and the dark yellow centre, surrounded by a zigzag line, acts as a guide directing the insect towards the nectar source inside the flower’s central tube. The resulting fruit is a dry, triangular capsule or pod, four to seven centimetres long, containing numerous pale brown seeds. These seeds float and are dispersed by water. They germinate in spring or early summer, either while still floating or on mud. Plants can also spread vegetatively, by growth from the underground rhizome. The same plant may eventually cover a region up to 20 m in radius. While it is primarily an aquatic plant, the rhizomes can survive prolonged dry conditions.

Yellow Iris has been used as a form of water treatment due to its ability to absorb heavy metals through its roots.  It is also thought to be the inspiration for the fleur-de-lis symbol, used in heraldry and by the Scouts Association.

Share This