Rorippa sylvestris (L.) Besser

Common Name: Keek

Synonyms and Other Names:

Radicula sylvestris; Keek; Yellow fieldcress

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Stems - Herbaceous, erect, from rhizomes, glabrous, green or becoming purple in the strong sun, ribbed, to +/-35cm tall, branching (Missouri Flora Web).

Leaves - Alternate, petiolate, deeply pinnatifid. Basal leaves to -10cm long, 2-2.5cm broad, with +/-6 main divisions per side. Cauline leaves similar but reduced. All leaves glabrous or with very few short hairs. Divisions of the leaves toothed. Upper leaves with thinner and fewer divisions than the lower. Tissue connecting the divisions of the leaves 0.2-0.3mm broad (Missouri Flora Web).

Inflorescence - Terminal and axillary racemes to +10cm long. Axis glabrous. Pedicels to 4mm long in flower, expanding to +/-1cm long in fruit, glabrous. Inflorescence compact in flower, quickly expanding. Siliques to 1cm long, 1mm in diameter, cylindric but slightly compressed, glabrous, with a beak to 1mm long (Missouri Flora Web).

Flowers - Petals 4, distinct, spatulate, yellow, glabrous, to +4mm long, 1.5mm broad, rounded at the apex. Stamens 6, erect, 4 larger and 2 smaller. Filaments yellow, glabrous, to 3mm long. Anthers yellow, 1mm long. Ovary cylindric, green-yellow, glabrous, 2mm long in flower, superior. Style .5mm long. Stigmas globose-capitate, .7mm broad. Sepals 4, distinct, yellow, erect to spreading, cupped, mostly glabrous but often with a few hairs at the apex externally, entire, 2-2.5mm long, to 1mm broad, subulate (Missouri Flora Web).

Size: maximum height: 0.7 feet.

Native Range: USDA ARS (National Genetic Resources Program) cites native range as western Asia, Caucasus, Northern Europe, Middle Europe, east Europe, East Europe, Southeastern Europe, and Southwestern Europe.

Great Lakes Nonindigenous Occurrences: This species has been in the U.S. since about 1818 (Elmore, 1998). The species first invaded the northeast then spread into the Great Lakes states and now is showing up in the midwest and west, with the most recent new occurrences arriving in the Pacific northwest (USDA, 2008; Elmore, 1998). It is now found as an invasive throughout most U.S. states, including the Great Lakes states IL, IN, MI, MN, NY, OH, PA, and WI (USDA, 2006).

It is conservatively estimated that more than half of the 81 ecoregions have been invaded by R. sylvestris in the United States. Notable exceptions include Texas, Oklahoma, Florida, Georgia, South Carolina, Nevada, South Dakota, and Wyoming, although this may reflect inadequate sampling effort (USDA, 2008).

The first Great Lakes sighting occurred in 1884 near Lake Ontario.

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 Rorippa sylvestris are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IN199220084Little Calumet-Galien; St. Joseph; St. Marys; Upper Maumee
MI1891201811Betsie-Platte; Boardman-Charlevoix; Detroit; Great Lakes Region; Lower Grand; Saginaw; Southeastern Lake Michigan; St. Clair; St. Clair-Detroit; Upper Grand; Western Lake Erie
MN195520082Beaver-Lester; St. Louis
NY188420089Cattaraugus; Eastern Lake Erie; Great Lakes Region; Lake Ontario; Lower Genesee; Oneida; Oswego; Seneca; St. Lawrence
OH192720089Auglaize; Cedar-Portage; Cuyahoga; Lake Erie; Lower Maumee; Ottawa-Stony; Sandusky; Southern Lake Erie; Western Lake Erie
PA200820081Lake Erie
WI200820086Lake Superior; Manitowoc-Sheboygan; Northwestern Lake Michigan; Pike-Root; Southwestern Lake Michigan; Upper Fox

Table last updated 5/25/2024

† Populations may not be currently present.

Ecology: Habitats are disturbed wetlands, including muddy or grassy borders of ditches, soggy meadows in floodplain areas, and poorly drained areas along railroads. Flowering from May-September.

Means of Introduction: Solid ballast. Tiny seeds can likely float on water or blow about in the wind. R. sylvestris is believed to spread rapidly at times of fast creek flow in autumn and winter in South Australia when rhizomes can fragment and spread downstream (Woldendorp and Bomford, 2004). In the United States, Emore (1998) has documented vegetative material (rhizomes) of the weed being shipped within the roots of herbaceous ornamentals, such as lilies, daylilies, and hosta.

Status: Established.

Great Lakes Impacts:
Summary of species impacts derived from literature review. Click on an icon to find out more...


Current research on the environmental impact of Rorippa sylvestris in the Great Lakes is inadequate to support proper assessment.
Rorippa sylvestris is allelopathic, inhibiting the germination of seeds of many other plants (Yamane et al 1992). Described as a pioneer species, it does not generally outcompete dense, established natives. R. sylvetris is known to hybridize with other members of the genus, but the degree to which it will hybridize with Rorippa spp. native to the Great Lakes region (e.g., R. curvipes, R. palustris, R. sessiliflora, R. sinuate) is unknown. 

There is little or no evidence to support that Rorippa sylvestris has significant socioeconomic impacts in the Great Lakes.
Rorippa sylvestris is designated as a noxious weed and is considered a serious pest to horticulture (ornamentals) and potential threat to crop and grazing lands. It can reduce bulb crop value and marketability as a contaminate of nursery stock.

There is little or no evidence to support that Rorippa sylvestris has significant beneficial impacts in the Great Lakes.

Management: Regulations (pertaining to the Great Lakes region)
There are no known regulations for this species.

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

Once established, this plant is very difficult to control.

Readily re-grows from rhizome fragments – most attempts at physical control only exacerbate the problem when small fragments are missed and regrow.

Pre-emergent herbicides suppress top growth but do not kill rhizomes which quickly produce new plantlets in response to the loss of the top. Glyphosate is marginally effective.  Selective post-emergent herbicides are not available. (NC State 2012)

Preemergence control was excellent with dichlobenil granules at 3 or 6 lb/A, isozaben at 1 or 2 lb/A and a geotextile/herbicide (17.5% Trifluralin). The geotextile fitted as collars alone were not effective. Trifluralin incorporated into the surface 2 inches at 2 lb/A was effective but did allow some emergence. Trifluralin plus isoxaben or oryzalin plus isoxaben were also effective at rates of 2 plus 0.5, 4 plus 1, or 6 plus 1.5 lb/A, or 3 plus 1, 4.5 plus 1.5, or 6 plus 2 lb/A, respectively, of the two herbicide combinations. Metolachlor at 3, 4.5, or 6 lb/A was ineffective for preemergence control of 3 cm rhizome pieces. Post emergence control was not commercial with 2,4-D, triclopyr, clopyralid or a combination of the latter two, when treated in the 6 to 8 leaf stage with 0.25% or 0.5% solutions. (Elmore et al 1996)

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

Remarks: Unlike many other members of the mustard family, the yellow cresses are largely restricted to wetland habitats.

References (click for full reference list)

Other Resources:
USGS/NAS Technical Species Profile

NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. Available (Accessed:  July 24, 2008).  

USDA, NRCS. 2008. The PLANTS Database. USDA Natural Resources Conservation Service (USDA, NRCS). National Plant Data Center, Baton Rouge, Louisiana 70874-4490 USA. Available online:  

Missouri Flora Web.

Author: Cao, L., and R. Sturtevant

Contributing Agencies:

Revision Date: 8/9/2019

Citation for this information:
Cao, L., and R. Sturtevant, 2024, Rorippa sylvestris (L.) Besser: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 8/9/2019, Access Date: 5/26/2024

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.