Butomus umbellatus L.

Common Name: Flowering rush

Synonyms and Other Names:

Grassy rush; Water gladiolus; Butomus junceus Turcz.

Leslie J. Mehrhoff, University of Connecticut, Bugwood.orgCopyright Info

Leslie J. Mehrhoff, University of Connecticut, Bugwood.orgCopyright Info

Identification: Butomus umbellatus is a moderately tall, rush-like perennial. Its leaves are basal originating from a stout rhizome that is stiff and erect when immersed or lax and floating when in deep water. The inflorescence is a many-flowered umbel borne. The flowers are perfect, regular, 2-3 cm across, and pink. There are 3 sepals, which are petaloid. There are 3 petals and 9 stamens with elongate anthers. It has 6 pistils that are simple, whorled, and united at the base. Its fruit is an indehiscent, many-seeded capsule (GISD, 2005).

Size: up to 1.5 m high

Native Range: Africa, Asia, and Eurasia (USDA NRCS, 2008)

Great Lakes Nonindigenous Occurrences: First observed in 1897 in North America. Widespread in the northeast US.  Locally abundant in northern US. Recorded in: CT, ID, IL, IN, ME, MI, MN, MT, ND, NE, NY, OH, PA, SD, VT, WI (USDA NRCS, 2008)  Canada: Alta., Man., N.S., Ont., P.E.I., Que.

Great Lakes Region: It was first collected near Laprairie on the St. Lawrence River in 1905; a specimen in the Britton Herbarium at the New York Botanical Garden was collected September 16, 1906, by Fr. Louis Arsene on the borders of the St. Lawrence River. West of Niagara Falls, the taxon was first collected near Detroit (Wayne County, Michigan, in Brownstown Township and at River Rouge) in 1930 by O. A. Farwell, although he noted on the specimen, "Has been here since before 1918!!!" (R. L. Stuckey 1968).  Studies of Butomus in North America (L. C. Anderson et al. 1974) indicated that apparently the genus has become naturalized in North America at two separate locations, one near Detroit and another in the St. Lawrence River region. It is possible that plants naturalized in the St. Lawrence River region originated in eastern Asia, and those naturalized in the Detroit area originated in Europe or western Asia.  Stuckey (1994) included dots for B. umbellatus from Indiana and British Columbia.   Now widespread in Great Lakes region.

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Butomus umbellatus are found here.

Full list of USGS occurrences

State/ProvinceYear of earliest observationYear of last observationTotal HUCs with observations†HUCs with observations†
Indiana195219631St. Joseph
Michigan1905201723Au Sable; Betsy-Chocolay; Cass; Cheboygan; Clinton; Detroit; Huron; Kalamazoo; Kawkawlin-Pine; Lake Erie; Lake Huron; Lake Michigan; Lake St. Clair; Lone Lake-Ocqueoc; Lower Grand; Ottawa-Stony; Pere Marquette-White; Pigeon-Wiscoggin; Raisin; Saginaw; Shiawassee; St. Clair; St. Joseph
New York1929201415Chaumont-Perch; Great Lakes Region; Headwaters St. Lawrence River; Lake Champlain; Lake Ontario; Mettawee River; Niagara; Northeastern Lake Ontario; Oak Orchard-Twelvemile; Oswego; Raisin River-St. Lawrence River; Richelieu River; Salmon-Sandy; Seneca; St. Lawrence
Ohio193320174Cedar-Portage; Lake Erie; Ottawa-Stony; Western Lake Erie
Pennsylvania194120152Chautauqua-Conneaut; Lake Erie
Vermont192720073Lake Champlain; Mettawee River; Otter Creek
Wisconsin197520178Fox; Lake Michigan; Lake Winnebago; Oconto; Peshtigo; Pike-Root; Upper Fox; Wolf

Table last updated 6/21/2018

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: Butomus umbellatus grows in lakes, riparian zones, water courses, wetlands, and marshes. It can tolerate water as deep or deeper 2 meters, where cattail is normally found, and can extend to the deepest range of native emergent marsh species (except possibly for hard-stem bulrush and wild rice). Once established in a marsh, populations tend to increase and persist indefinitely. Water level fluctuations may promote the spread of B. umbellatus, allowing populations to expand when water levels are low and the soil surface is exposed and warmed (Hroudová et al. 1996). However, severe or long-lasting decreases in water level could result in the reduction of B. umbellatus populations (e.g., Hudon 2004). It is intolerant of salt or brackish water.

Butomus umbellatus is a perennial plant. It is in flower from July to September, and the seeds ripen from August to September (in North America). The scented flowers are hermaphroditic and are pollinated by bees, flies, and lepidopterans. Although Canadian populations of B. umbellatus appeared to be incapable of autonomous seed production (without external pollination assistance), plants were self compatible and produced more seed when self-pollinated (Eckert et al. 2000).

Flowering rush can be fertile (both spread by sexual reproduction and seeds or by vegetative means) or sterile (can only reproduce by vegetative means (Lui et al. 2005, Parkinson et al. 2010). Diploid populations of B. umbellatus can reproduce sexually via seed production and clonally via the branching and fragmentation of rhizomes and the production of small bulbils on both the rhizomes and inflorescences (Lui et al. 2005). Most B. umbellatus populations in the Great Lakes are diploid and capable of producing abundant viable seed, although the major method of reproduction appears to be clonal (Lui et al. 2005). Sterile triploid populations of B. umbellatus also exist in the Great Lakes region. North American triploid populations rarely flower and also have a limited ability to multiply and disperse via clonal reproduction, although they may have a greater ecological tolerance than diploid populations as a result of polyploidy or of greater investment in vegetative growth (Lui et al. 2005). Triploid populations also appear to be spread more commonly through the horticulture trade. Lui et al. (2005) suggested that these different reproductive strategies are indications of two different forms of B. umbellatus in North America with different life histories and invasion histories.

Diploid and triploid populations of B. umbellatus exist throughout its global range, although reproductive traits and strategies may differ by region (e.g., North American vs. European populations) (Hroudová and Zákravský 1993, Lui et al. 2005). Relative to native European populations, Brown and Eckert (2005) found that nonindigenous North American diploid populations invested much more biomass in reproduction and were more likely to produce both inflorescences and clonal bulbils. Post-establishment survival was also over twice as high for North American populations as it was for European populations (Brown and Eckert 2005).

Flowering rush has a very wide range of hardiness (zones 3-10) which makes it capable of being widely invasive in the United States (IPANE 2001).


Means of Introduction: Butomus umbellatus was intentionally brought to North America from Europe as a garden plant for ornamental purposes. Ship ballast has also been cited as a potential vector for the initial introduction. 

It can be spread over long distances by garden planting, and once established in a watershed, it spreads locally by rhizomes and by fragmentation of the root system. Muskrats reportedly use parts of the plant and contribute to its local spread, though the importance of this particular vector in spreading has not been investigated (Staniforth and Frego 1980). Populations may be spread via the horticulture trade (Lui et al. 2005), and boaters can also transport flowering rush on their equipment.  Water and ice movements can easily carry it to new areas of a water body (Proulx 2000).

Status: Butomus umbellatus is a prohibited species in Illinois, Michigan, and Minnesota, and is restricted in Wisconsin (GLPANS 2008). A recent survey of Minnesota Nursery and Landscape Association Members revealed that 80% of respondents were incorrect or unsure of the non-native character of B. umbellatus despite its prohibited status in Minnesota (Peters et al. 2006).

Actively expanding (EPA 2008).

Great Lakes Impacts:  

Butomus umbellatus has a moderate environmental impact in the Great Lakes.

Flowering rush was found at a third of sampled coastal wetlands on Lake Erie and Lake Ontario, although it was never a dominant species where it was documented (Trebitz and Taylor 2007). However, in southern Lake Champlain, B. umbellatus forms dense stands that appear to displace native species (Marsden and Hauser 2009).

Based on the expert judgment of Canadian botanists, flowering rush has been assessed as a limited to moderate-impact species with spreading activity in Canada (White et al. 1993). Sampling along the St. Lawrence River in Quebec suggested that B. umbellatus was less common than purple loosestrife (Lythrum salicaria) but tended to be much more invasive when present. At about 40% of the sites at which it was found, B. umbellatus made up more than 50% of the total species cover, suggesting that it is capable of dominating wetland sites (Lavoie et al. 2003). However, Shannon diversity indices and number of native plant species were still greater at sampling stations with B. umbellatus than at stations with Phalaris arundinacea and Phragmites australis (Lavoie et al. 2003). Lavoie et al. (2003) speculated that even the densest populations of flowering rush may leave some space available for native species as a result of its particular growth form.

Butomus umbellatus can displace native riparian vegetation via competition and could diminish native biodiversity as a result (MPLP 2006). It is capable of forming dense mats that could affect the availability of light, nutrients, and dissolved gasses in colonized waters (MPLP 2006). Infestations could also result in increased water temperatures and altered nutrient flows and/or sedimentation rates (Rice and Dupuis 2009). In the western U.S., emergent monocultures have colonized and reduced areas of open water; although scientific study is limited, these invasions have reportedly increased sedimentation, reduced water flow in canals, and modified the physical structure of previously unvegetated localities (Rice and Dupuis 2009).

Current research on socio-economic impact of Butomus umbellatus in the Great Lakes is inadequate to support proper assessment.

Wild rice (Zizania aquatica) has been identified as a species potentially threatened by the spread of B. umbellatus in the wetlands of the northern United States and Canada (Lui et al. 2005, MPLP 2006). Reduction in wild rice harvests could affect indigenous people who live in the area (B. Ranta pers. comm. to Lui 2001).

Stands of B. umbellatus can become thick and undesirable, even in its native range (Hroudová et al. 1996). Butomus umbellatus can obstruct irrigation canals and interfere with industrial shoreline uses, boat traffic, and other recreational activities (Eckert et al. 2000, MPLP 2006). Flowering rush has reduced water delivery in the irrigation ditches of the Flathead Valley (MT) and the Aberdeen-Springfield (ID) canal system (Rice and Dupuis 2009). In the latter, B. umbellatus has colonized an estimated 150 miles of the 300 mile main canal, threatening water availability for potato and cash crops and requiring removal every 2 or 3 years. Full management of flowering rush in this canal system could raise costs to farmer shareholders by as much as 8% (Rice and Dupuis 2009). Flathead Lake (MT) has been infested by monocultures of flowering rush that have inhibited boat passage and reduced open water availability for swimming and fishing. Further concerns have arisen regarding the role of B. umbellatus populations as an ideal habitat for the great pond snail (Lymnaea stagnalis), an intermediate host of a trematode (Trichobilharzia ocellata) responsible for swimmer’s itch (Rice and Dupuis 2009).

Current research on the beneficial effect of Butomus umbellatus in the Great Lakes is inadequate to support proper assessment.

Muskrats use parts of the plant for habitat, and ducks reportedly graze on B. umbellatus in its native range (Hroudová et al. 1996). Flowering rush could also provide structural habitat for some fish species, particularly those that depend on vegetation for spawning (Rice and Dupuis 2009).

It has been used as an aquatic ornamental plant, though it is now prohibited in several Great Lakes states (GLPANS 2008, Les and Mehrhoff 1999). The roots and seeds of B. umbellatus are edible, and the plant has been investigated for some medicinal uses (e.g., anti-microbial properties were tested but not discovered) (Özbay and Alim 2009).


Regulations (pertaining to the Great Lakes region)
Butomus umbellatus is listed as a prohibited species in Michigan, Minnesota, and Illinois, and as a restricted species (but still available) in Wisconsin (GLPANS 2008, Jensen 2011). A recent survey of Minnesota Nursery and Landscape Association Members revealed that 80% of respondents were incorrect or unsure when judging the non-native status of B. umbellatus despite its prohibited use in Minnesota (Peters et al. 2006). It is on New York State’s Interim Invasive Species Plant List (NYDEC 2011). In Pennsylvania it is labeled as a medium-high threat to native ecosystem and in Ohio it is classified as a “well established invasive plant” (Higman and Campbell 2009, Ohio 2000).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

Butomus umbellatus has a similar appearance to some native plants, such as common bulrush (Typha latifolia) (Jensen 2011). Care should be taken to first identify the plants in question before control actions are taken.

In its native range in Europe, ducks have been known to graze extensively on flowering rush (Hroudová et al. 1996).

Butomus umbellatus spreads by floating seeds and vegetatively by rhizomes and root pieces (Campbell et al. 2010, Jensen 2011). Great care to remove all parts of the plant should be taken when implementing a physical method of control. To ensure removed plants will not sent out shoots, thoroughly dry all plant pieces (Jensen 2011).

Cutting flowering rush below the water surface will not kill the plant, but it will reduce its abundance, and therefore, its ability to spread. Multiple cuts may be needed throughout the growing season (Jensen 2011). Cutting later may remove most of that season’s rhizome growth (Hroudová et al. 1996). Hand digging may be a viable option for removing isolated plants (Jensen 2011). Techniques involving raking or pulling are not recommended (Jensen 2011).

Decreases in water level promotes establishment of flowering rush, suggesting that water level reductions is not a method of control (Parkinson et al. 2010).

Control with the use of herbicides is difficult because these chemicals easily miss or fall off of the narrow, slightly twisted leaves of flowering rush (Parkinson et al. 2010, Seizer 2009). There is currently no herbicide that targets B. umbellatus, but initial testing shows that a mid-summer application of imazapyr (labeled as the herbicide ‘Habitat’) during calm weather may be effective (MNDNR 2012, Parkinson et al. 2010).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

Remarks: The name Butomus umbellatus forma vallisneriifolius (Sagorski) Glück has been used for plants that grow totally submersed or have floating leaves. Field transplant experiments with North American plants (R. L. Stuckey et al. 1990) have demonstrated that the non-flowering submersed form can be converted to a flowering mudflat form, and that flowering terrestrial plants can be transformed into non-flowering submersed ones. Consequently, B. umbellatus f. vallisneriifolius is a deep-water growth form and should have no taxonomic systematic status. A map of Butomus in North America, prepared by R. L. Stuckey (1994), showed that he accepted two species. His map essentially had everything east of Niagara Falls as B. junceus and everything west of the Falls as B. umbellatus. At this time, experts do not accept two species in the genus.

References: (click for full references)

Brown, J.S. and C.G. Eckert. 2005. Evolutionary increase in sexual and clonal reproductive capacity during biological invasion in an aquatic plant Butomus umbellatus (Butomaceae). American Journal of Botany 92(3):495—502.

Campbell, S., P. Higman, B. Slaughter, and E. Schools. 2010. A Field Guide to Invasive Plants of Aquatic and Wetland Habitats for Michigan. Michigan DNRE, Michigan State University Extension, Michigan Natural Features Inventory. 90 pp.

Delisle, F., C. Lavoie, M. Jean, & D. Lachance. 2003. Reconstructing the spread of invasive plants: taking into account biases associated with herbarium specimens. Journal of Biogeography 30:1033—1042.

Eckert, C.G., B. Massonnet, J.J. Thomas. 2000. Variation in sexual and clonal reproduction among introduced populations of flowering rush, Butomus umbellatus (Butomaceae). Canadian Journal of Botany 78(4):437 —446.

Flora of North America.  2008.  www.eFloras.org.

Global Invasive Species Database. 2005. Available http://www.issg.org/database/species/ecology.asp?si=610&fr=1&sts=sss&lang=EN. Accessed 19 September 2011. 

Great Lakes Panel on Aquatic Nuisance Species (GLPANS). 2008. Prohibited species in the Great Lakes region. Research Coordination Committee, GLPANS. Available: http://www.glc.org/ans/pdf/08-11-26-Great%20Lakes%20Reg%20Species%20List-complete.pdf

Higman, P., and S. Campbell. 2009. Meeting the Challenges of Invasive Plants: A Framework for Action. Michigan Department of Natural Resources Wildlife Division. Lansing, Michigan. 87 pp.

Hroudová, Z. and P. Zákravský. 1993. Ecology of two cytotypes of Butomus umbellatus II. Reproduction, growth and biomass production. Folia Geobotanica and Phytotaxonomica 28(4):413—424.

Hroudová, Z., A. Krahulcová, P. Zákravský, V. Jarolímová. 1996. The biology of Butomus umbellatus in shallow waters with fluctuating water level. Hydrobiologia 340:27—30.

Hudon, C. 2004. Shift in wetland plant composition and biomass following low-level episodes in the St. Lawrence River: looking into the future. Canadian Journal of Fisheries and Aquatic Sciences 61(4):603—617.

Invasive Plant Atlas of New England (IPANE). 2009. University of Connecticut. Available http://www.eddmaps.org/ipane/. Accessed 5 April 2012.

Jensen, D. 2011. Flowering rush (Butomus umbellatus). Minnesota Sea Grant. Available http://www.seagrant.umn.edu/ais/floweringrush. Accessed 20 March 2012.

Lavoie, C., M. Jean, F. Delisle, and G. Létourneau. 2003. Exotic plant species of the St Lawrence River wetlands: a spatial and historical analysis Journal of Biogeography 30: 537—549.

Les, D.H., and L.J. Mehrhoff. 1999. Introduction of Nonindigenous Aquatic Vascular Plants in Southern New England: A Historical Perspective. Biological Invasions 1(2): 281-300.

Lui, K. 2001. Genetic causes & consequences of variation in sexual fertility amoung introduced population of clonal aquatic plant Butomus umbellatus (Butomaceae). Master of Science Thesis. Queen's University Kinsgton, Ontario, Canada. 126 pp.

Lui, K., F.L. Thompson, and C.G. Eckert. 2005. Causes and consequences of extreme variation in reproductive strategy and vegetative growth among invasive populations of a clonal aquatic plant, Butomus umbellatus L. (Butomaceae). Biological Invasions 7:427—444.

Manitoba Purple Loosestrife Project (MPLP). 2006. Flowering rush, an invasive plant found in Manitoba: Butomus umbellatus. Invasive Species Council of Manitoba. Available http://www.invasivespeciesmanitoba.com/site/uploads/pdf/fs_flowrush.pdf. Accessed 2011.

Marsden, J.E., and M. Hauser. 2009. Exotic species in Lake Champlain. Journal of Great Lakes Research 35: 250—265.

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Rice, P. and V. Dupuis. 2009. Flowering rush: an invasive aquatic macrophyte infesting the headwaters of the Columbia River system. Center for Invasive Plant Management (CIPM), Montana State University, Bozeman, MT. 11 pp.

Seizer, M. 2009. The Michigan Department of Environmental Quality Biennial Remedial Action Plan Update for the River Rasion Area of Concern. Water Bureau, Aquatic Nuisance Control & Remedial Action Unit: Michigan DEQ, Lansing, MI. 15 pp.

Staniforth, R.J. and K.A. Frego. 1980. Flowering rush (Butomus umbellatus) in the Canadian prairies. Canadian Field-Naturalist 94(3):333—336.

Trebitz, A.S. and D.L. Taylor. 2007. Exotic and invasive aquatic plants in Great Lakes coastal wetlands: distribution and relation to watershed land use and plant richness and cover. Journal of Great Lakes Research 33:705—721.

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Author: Cao, L., L. Berent, and A. Fusaro

Contributing Agencies:

Revision Date: 4/9/2018

Citation for this information:
Cao, L., L. Berent, and A. Fusaro, 2018, Butomus umbellatus L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI, https://nas.er.usgs.gov/queries/greatlakes/FactSheet.aspx?SpeciesID=1100&Potential=N&Type=0&HUCNumber=DGreatLakes, Revision Date: 4/9/2018, Access Date: 6/21/2018

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.