Flowering-rush
Butomus umbellatus

Flowering-rush is an aquatic plant found along lakeshores and slow-moving rivers, and in water up to 9 feet deep. Although it resembles a true rush, flowering-rush is in its own family and can be distinguised by its attractive pink flowers. Native to Eurasia, flowering-rush was introduced first to the eastern United States and Canada as an ornamental and continues to be brought in to the country as an ornamental. It has spread to large areas of Canada and the northern United States. It is currently known from only a few locations in Washington State, including a large infestation on Silver Lake in Whatcom County, Washington. It impacts both the ecological and recreational values of shallow water and shorelines.

Flowering-rush is a Class A Noxious Weed in Washington State due to its limited distribution in the state and the potential for significant impact to state resources. Public and private landowners are required to control this plant when it occurs on their land. Because of the difficulty in distinguishing this plant from native rushes and bulrushes, we recommend contacting the noxious weed program for a positive identification before removing. There are currently no records of this plant in King County, so if you do find flowering-rush in King County, please report the location right away.

Identification (see below for more photos)

Leaves are thin, straight, sword-shaped, triangular in cross-section, and up to 40 inches long
Flowering plants can be up to 5 feet tall
Flowers grow on tall, cylindrical stalks in round-topped umbrella-like clusters of 20-50 flowers
Flowers have three large pink petals (the three sepals under the petals are also pink and look like small petals)
In deeper water, the plant grows submerged with floating leaves
Bloom time is June to August
Resembles bulrushes and true rushes when not in flower
Bulbils (little bulb-like plant sprouts) may be present at the base of flower stalks and at the roots
Rhizomes are fleshy and grow trailing along the ground

Habitat and Impact

Flowering-rush grows along lakeshores and slow-moving rivers. It can be found from the shoreline and in water up to 9 feet deep. Flowering-rush has been expanding in range since it was introduced in the early 1900's to the eastern United States and Canada, and can now be found in many of the states and provinces along the US-Canada border. It is limited to a few locations in Washington State but has proven very challenging to remove once it is established. Flowering-rush competes with native wetland and shoreline vegetation and can crowd out more desireable species.

Growth and Reproduction

Flowering-rush produces numerous pea-sized bulbils that easily detach from the rhizome and are dispersed by the water. They quickly germinate on the soil or water surface and produce new plants. Flowering-rush also produces bulbils at the base of the flower stalks that also fall off and grow into new plants. Some varieties of flowering-rush produce seeds as well, but some do not. Flowering-rush also spreads through rhizomes and rhizome branches that break off to form new plants.

Flowering-rush has two growth forms. In shallow water or along shorelines, plants have stiff, upright leaves. In deeper water, the plants grow submerged and have flexible floating leaves that reach the surface and move with the water.

Control

Prevention: Flowering-rush is sometimes sold for water gardens, so be careful to check the Latin names of plants you are buying to avoid introducing this species. When flowering-rush is present, take care not to disturb the soil as this will spread rhizome bulbils and fragments. Also, remove plants before they seed to prevent spread and do not allow any pulled plant material to return to the water.

Small patches: Plants can be carefully dug up, although care needs to be taken to avoid spreading bulbils present at the roots and at the base of the flower clusters.

Larger patches: Controlling this species is very challenging due to its many ways of reproducing. Permits will also be needed since this plant grows in water. Please check with your local permitting office for more information. Testing is being done to determine the most effective chemical treatment for this species. Preliminary testing reported by Minnesota Department of Natural Resources suggests that treating with imazapyr (Habitat) in mid-summer during calm wind conditions may be effective. Please refer to herbicice labels for site specific control information and refer to the PNW Weed Management Handbook for additional information on herbicide use.