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flowering rush (Butomus umbellatus)
USDA symbol: BUUM

ODA Rating: A

Flowering rush risk assessment
Noxious weed listing process

Other common names
grassy rush and water gladiolus

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Images courtesy of Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

If images are downloaded and used from the ODA web site please be sure to credit the photographer.

Flowering rush is a perennial aquatic plant in the family, Butomaceae and not a true rush species. This weed is distinctive and easy to identify when flowering, difficult when not in flower. It is a tall plant growing to a height of 1.5 meters in marshes and in aquatic habitats. The plant crown is topped by an umbel of showy-white or pink flowers that emerge in late summer to early fall. The flowers consist of three petal-like sepals with no real petals present. Leaf stems are triangular in cross-section. Flowering rush can grow either as an emergent in meter deep water or in the lower marsh. Plants growing in these two environments acquire two distinct growth forms. The aquatic morph has limp, narrow leaves and doesn’t flower. The emergent form has stiff narrow leaves growing rigid and upright. Flowering rush reproduces both asexually by rhizomes and bulblets and sexually through seed production. Seed production only occurs in diploids as well as greatly increased bulblet production. Triploid plants reproduce entirely by bulblets and rhizomes though to a much lesser degree (Brown and Eckert 2004). Diploid plants dominate in North America. Moving water is the predominant dispersal mechanism for localized as well as long-distant weed movement, human activities and wildlife also contribute.

Literature indicates a range of concern about the impact on wetlands in North America. Authors state that the plant has the potential to invade and disrupt native marshlands. Anderson et al describe flowering rush out-competing cattails and willows in Idaho but data from the St. Laurence River shows that even at high infestation levels, native plant diversity has not been seriously affected. Rice and Dupuis have demonstrated that the species is truly capable of forming vast monocultures in literal zones as well as dominating intact marshlands. In the lower Columbia, it may compete strongly with reed canary grass.  Evidence of economic damage is now emerging in the western United States.  Unlined irrigation canals are becoming clogged as well as drainage ditches. Maintenance of these structures is expensive. Public and private boat access is now being impeded at some locations in Idaho (Rice 2008). It is unclear at this time of the effects on fishing access and success. Shallow lakes could become seriously infested and rendered unfishable. Reservoirs with variable water levels provide great habitat for this species. Large literal zones previously uncolonized by plants can be expected to become monocultures of Butomus.

Flowering rush was first discovered in North America about 1879 along the St. Laurence River, it has spread throughout the river into the Great Lakes and sporadically across the Northern United States and Southern Canada (Brown & Eckert 2004). Its preferred habitat is lake shorelines and slow moving waters to a depth of around two meters. Flowering rush densities can be quite variable from scattered clumps to populations exceeding 50% cover in the St. Laurence waterway (Lavoie et al.2003). It has been documented in Idaho (Rice & Dupruis 2008) and Montana though populations in Western North American are still limited. Infestations have been located in Washington State but are rare.

Distribution in Oregon
Currently there are no known sites of flowering rush located in Oregon. The Columbia River system is considered highly susceptible to invasion.

Biological controls
Biological control agents are not used on "A" listed weeds in Oregon. This weed is being managed for eradication.
Informational links:
Oregon Weedmapper
Printable trifold flowering rush brochure (pdf)