Yellow flag iris (Iris pseudacorus) is a robust, clumping perennial herb that is easy to identify in flower, since it is the only totally yellow-flowered Iris in wildlands in British Columbia. At maturity, it grows to 40 cm to 1.5 metres tall.
Iris pseudacorus is native to Europe and the British Isles, Western Asia, North Africa, and the Mediterranean region. It grows in a variety of fertile, low-lying wetland habitats including river banks, ponds, lakes and marshes (both freshwater and saltwater). It can reproduce via seed or rhizome. Yellow flag forms dense colonies that invade and dominate a variety of vegetation types, displacing native plant and animal diversity, and altering natural succession.
Manual or mechanical methods that remove the entire rhizome mass can successfully control small, isolated patches. Pulling or cutting I. pseudacorus plants may provide adequate control, but only if it is repeated every year for several years to weaken and eventually kill the plant. Dead-heading (removing the flowers and/or fruits) plants every year can prevent seed development and seed dispersal, but will not kill the plants. Yellow flag iris will sicken livestock if ingested, and is generally avoided by herbivores (although muskrats will eat the rhizomes). Contact with the resins can cause skin irritation in humans, so it’s important to wear gloves and cover skin when pulling, cutting, or digging.
Alternatives for planting:
- Oregon iris (Iris tenax)
- wild iris (Iris setosa)
- western blue iris (Iris missouriensis)
- skunk cabbage (Lysichiton americanum)
Several flowers can occur on each stem, along with one or two leafy bracts. Each flower resembles a common garden iris. The leaves are mostly basal and are folded and clasp the stem at the base in a fan-like fashion. Yellow flag iris is perennial, and will remain green during winter where the weather is mild. It has stout rhizomes and long, spreading roots. Seeds form in large, glossy green, triangular capsules. The seeds are corky. The plants spread rhizomatously and grow tightly bunched together.
This is the only yellow iris found in BC’s wet areas, but when not flowering it may be confused with look-alike cattail (Typha latifolia). Look for the fruits in the summer, or the fan-shaped plant-base at other times of year.
On the photo below the iris is on the left - look for a flat fan of leaves that's bright green. On the right is cattail - look for leaves that originate from a rounded stalk with leaves that are grey-green.