Yellow flag iris is a highly invasive plant that forms dense stands in wetland areas, along lakeshores, and on the margins of rivers and streams. It outcompetes native species, disrupts water flow, and alters the natural structure of waterways.

The plant can invade pastures, displace native vegetation, and is toxic to livestock. Its seeds are buoyant, easily dispersed by water, and can remain viable for over a year, making the plant difficult to control once established. Yellow Flag Iris negatively impacts the ecological health of water bodies, cultural values, and agricultural productivity.

Yellow Flag Iris is found across Otago, including Mosgiel, Lake Wānaka, Lake Whakatipu,  Lake Hayes, Tahakopa Estuary in Papatowai, and Oamaru. 

• Size: Grows up to 1.5 metres tall.
• Leaves: Broad, flat, sword-shaped leaves forming a fan from the base of the plant.
• Flowers: Bright yellow flowers up to 12 centimetres in diameter with three large drooping sepals (leaves that form the outermost layer of a flower) and three smaller, upright petals.
• Root system: Thick, fleshy rhizomes form dense mats that can float in water or anchor in wet soil.
• Similar species: It looks similar to stinking iris (Iris foetidissima), which gives out a foul smell when crushed, and Typha orientalis (Raupō), which has different flower heads and taller stems.
• Habitat: Commonly found along the edges of lakes, rivers, wetlands, and drainage systems. It thrives in both fresh and brackish water environments.

Yellow Flag Iris is most visible when flowering from October till December. 

Yellow flag iris is declared an unwanted organism in the National Pest Plant Accord (NPPA).  Any species declared a pest under the NPPA cannot be sold or be in a place where plants are being sold. Pest plants cannot be propagated, bred, multiplied, communicated, released, caused to be released, or otherwise spread. 

Do not attempt to undertake control of yellow flag iris yourself. Report any sightings to Otago Regional Council.

www.orc.govt.nz/yellowflagiris