Scientific name: Butomus umbellatus

What Is It?

Flowering rush is a perennial freshwater aquatic plant that grows in lakes, rivers, and wetlands. It spreads quickly through bulbils (small bulb-like structure), and fragments of the rhizomes (a type of underground stem).

Is It Here Yet?

It is established in the upper Columbia River watershed, the lower Yakima River, and the Spokane River. Flowering rush threatens the entire downstream Columbia River system due to its ability to spread easily on water currents. It is also in Pierce and Whatcom Counties in western Washington.

Why Should I Care?

It can out compete native plants and create areas where no other plants can grow. It reduces recreational opportunities by clogging water bodies making boating and swimming difficult, and has been linked to swimmer’s itch. It provides cover and nesting habitat for invasive fish that eat desirable native fish such as salmon and trout. It impedes water delivery in irrigation canals and is difficult and costly to control.

How Can We Stop It?

Flowering rush is incredibly difficult to control, and efforts to contain it have so far been unsuccessful. It can be dug out manually, but the difficulty lies in removing all of the rhizomes without dislodging any attached bulbils. Covering small patches with landscape mat also works if the plants are along the shore. Certain herbicides will reduce growth; however all herbicide use must be covered by permits.

What Are Its Characteristics?

  • Long, thin, triangular, sword-like leaves.
  • Flowering stalk can grow up to 5 feet tall.
  • Clusters of pink flowers with three petals and three smaller sepals (that resemble petals) below the true petals.

How Do I Distinguish It From Native Species?

Flowering rush is difficult to identify when not flowering; it blends in with other shoreline and aquatic vegetation. If not flowering, the presence of rhizomes and triangular leaves help identify it. The pink flowers are distinctive.

Additional Photos