Yellow Flag
Iris pseudacorusIridaceae
Whole Plant
Whole PlantFlowerFruitHabitat
Photos (c) Cheryl Comeau Beaton unless otherwise noted


  • Yellow iris

The Plant:

  • An upright, clumping herbaceous perennial with stout rhizomes, 3-4 feet tall.

The Leaves:

  • erect
  • arching tips
  • arise in a fan from the soil
  • long, dark, pointed
  • sword-shaped
  • raised mid-rib

The Flowers:

  • Pale to bright yellow very showy flowers, 2.75 to 3.5 inches wide. Each contains six clawed perianth segments, with three large downward-spreading sepals and three smaller erect petals. The yellow sepals have light-brownish to purple veins or flecks.

The Fruits:

  • glossy, green pods
  • large 4-8 cm
  • 6-angled and contain many flattened brown seeds

The Habitat:

  • wetland habitats
  • along river edges and pond shores, in floodplains
  • gardens
  • tolerates saline conditions and can be found on salt marsh edges


  • rhizomes and seeds can be transported by water
  • rhizomes are sometimes planted in gardens

Key ID Features:

  • arching tips
  • fan from soil
  • sword-like leaves
  • raised mid-rib
  • bright yellow
  • 3 downward facing sepals, 3 erect petals
  • 6-angled large pods

Similar Species:

  • This is the only yellow Iris in the United States, though when not in flower it can be confused with native irises such as Northern blue flag (Iris versicolor), which has a very similar leaf structure and size. Flower color is the key to distiguishing between the two.
  • Cat-Tails (Typha spp.) look similar in structure and height, but have distinctly different flowers.


  • Forms large clonal populations that displace native species
  • rhizomes can sustain drought conditions
  • seeds can survive burning
  • contains poisonous compounds which restricts grazing by animals
  • caution should be used during removal as skin irritation can occur
  • Any cultivated iris with significant yellow coloring is derived from this species and is therefore at risk of escaping from cultivation and spreading. People that do their own yard work may dump their yard waste in the Moors, thinking it is harmless mulch, leading to irises and other garden bulbs/corms sprouting up in natural places.

Growth Form: Herb

Origin: Asia, North Africa, Europe

Level of Invasiveness for Nantucket: Invasive

Level of Invasiveness for Massachusetts: Invasive

Massachusetts Cultivation Restrictions: importation ban July 2006, propagation ban January 2007

Credits: The Electronic Field Guide to the Invasive Plants of Nantucket (c) 2005-2006 Maria Mitchell Association, EFG Project, UMass Boston