Yellow Flag

Iris pseudacorus
Iris Family (Iridaceae)
Perennial Herb
Flowers: May–Jul
Native Range: Europe, North and West Africa

Introduction: as an ornamental in the mid 1800s.

Mid-Atlantic Range & Habitats: Marshes, wet meadows, shores.

Ecological Impacts

Yellow Flag invades shallow water areas, excluding other wetland plants and altering habitat by trapping sediment, which then leads to tree and shrub establishment. It is tolerant of salt, drought, and poor water quality, making it a good competitor in disturbed wetlands. The plant spreads rapidly by rhizomes and seed.

Quick ID

  • Flower color: Yellow
  • Fruit: Capsule 6-angled
  • Fruit: Capsule opening at maturity into 3 widely spreading segments

More ID Tips

Yellow Flag is the only naturalized yellow-flowered Iris in our region. Nevertheless, it is difficult to separate from the native Northern Blue Flag when the flowers are not present. Yellow Flag flowering stems tend to be shorter than or equal to the height of the leaves, while the stems of the Northern Blue Flag usually equal or exceed the length of the leaves. Yellow Flag may have slightly narrower leaves than Northern Blue Flag, but there is much overlap, so identification of flowering or fruiting plants is recommended.