Yellow iris (Iris pseudacorus)
Photo credit:  © abrideu/Flickr

Yellow Iris

(Iris pseudacorus)

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If you believe you have found this species anywhere in Pennsylvania, please report your findings to iMapInvasives by submitting an observation record.

Species at a Glance

This exotic member of the iris family, also called the yellow flag, is commonly found in wetland regions of the United States. It is an emergent aquatic perennial with showy yellow flowers that can grow on average 0.3-0.9 m (1- 3 ft) tall, although some can reach up to 2.1 m (7 ft).

Identification

Leaves: Long, broad, flattened, and sword-shaped leaves are usually dark green in color, pointed at the ends and overlapped at the base. Leaves can grow up to 2.5 cm (1 in) wide.

 

Flowers: There are usually 2-3 flowers on each stalk that have bright yellow to cream-colored petals with sepals outlined in purple and brown. They are 8 -10 cm (3.1-3.9 in) in diameter and bloom June through August.

 

Fruits/Seeds: Numerous smooth, flattened seeds grow in small oblong-shaped capsules that are roughly 5 cm (2 in) long. Capsules grow in clusters at the base of the flower and have the ability to float.

 

Stems/Roots: Fleshy and form from a single-branched stem. They are 10-30 cm (3.9-12 in) long.

Similar Species

Native look-a-likes include cattails (Typha spp.), bur-reeds (Spanganium spp.), and the blue flag iris (Iris versicolor). Cattails look similar during spring growth, except that their leaves are arranged in rounded layers rather than flat like the yellow iris. Native irises have thinner leaves and blue-purple flowers instead of yellow.

Habitat

The yellow iris is found mainly in wetland areas like marshes and the shores of lakes, ponds, and streams; however, they have a high tolerance for drought and can survive long periods in dry, acidic, and low-oxygen soils.

Spread

The yellow iris reproduces vegetatively through horizontal underground stems called rhizomes, which form into roots, allowing it to re-grow new plants.

Distribution

Native to Europe, western Asia, northern Africa, and the Mediterranean region, yellow iris was brought to the United States as an ornamental plant that quickly spread to uncultivated areas and is now established in over 40 states, Lake Erie, and throughout the entire Mid-Atlantic region.

 

Note: Distribution data for this species may have changed since the publication of the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016), the source of information for this description.

Environmental Impacts

The roots of the yellow iris are sturdy and connect hundreds of flowering plants underground, congesting water flow and leaving no room for native wetland plants to grow. It is also poisonous, harming fish and animals that touch or eat it. It can cause skin irritation when touched, so caution should be used when trying to remove it.

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Note

Information for this species profile comes from the Mid-Atlantic Field Guide to Aquatic Invasive Species (2016).