Yellow Flag Iris
Iris pseudacorus
Washington State Classification
Class C — Widespread, County-Selected Control
Yellow flag iris is an invasive ornamental perennial that is a problem in many states and other countries.
Quick Reference
Identification
Growth Habit
Yellow flag iris is a perennial, aquatic, herbaceous plant which grows 2 to 3 feet tall along shores in shallow water. Rhizomes spread and form large clumps.
Leaves
Stem and basal leaves present. Basal leaves are broad, flat, sword-shaped and stalkless. Stem leaves reduce in size going up the stem.
Flowers
Flowers few to several near stem ends. Flowers pale to dark yellow with brownish purple mottled markings. Flowers have 3 sepals and 3 petals, with petals shorter than sepals.
Fruit & Seeds
Capsules form from flowers, somewhat 3 angled and filled with flattened, D-shaped seeds.
Impact
Yellow flag iris is an invasive ornamental perennial that is a problem in many states and other countries. It will sicken livestock if ingested and is generally avoided by herbivores. Contact with its resins can cause skin irritation in humans.
Ecology & Spread
Habitat
Yellow flag grows in temperate wetlands along the margins of lakes and slow-moving rivers. It is most commonly found in very shallow water or mud. It tolerates drying and anoxic sediment and is also tolerant of some salinity, and high soil acidity. Please click here to see a county level distribution map of yellow flag iris in Washington.
Spread Mechanisms
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.
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Control Methods
Mechanical
- If pulling or digging yellow flag care should be used to protect the skin as resins in the leaves and rhizomes can cause irritation. Because rhizome fragments can grow to form new plants, all rhizome fragments must be carefully removed.