Disclaimer:

The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

---

Common name: keek

Synonyms and Other Names: Radicula sylvestris; Keek; Yellow fieldcress

Taxonomy: available through www.itis.gov

Identification:

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.

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

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.

Impact of Introduction: Considered a noxious weed in parts of the United States. It can form dense, tangled masses of stems and intertwining rhizomes floating in water or creeping over mud; rooted at several points, which may be several yards long (NatureServe. 2008). This species does not appear to have highly significant impacts, although it is expanding and becoming more noxious in the northeast (e.g. Hudson River basin) as well as in the Great Lakes, where it is considered an invasive aquatic species in some areas. In California and the Pacific Northwest, this species has recently emerged as an invasive pest with potential to invade natural systems through creeks when rhizome pieces (which can occur at depths up to 3 feet) fragment (Elmore, 1998).

In Germany, native Rorippa sylvestris hybridizes with non-native R. austriaca, forming Rorippa x armoracioides hybrids which appear to be more competitive/invasive than either of the parent species. Although both parents are present in the US and are likely to hybridize where they form contact zones, this potentially invasive hybrid has not yet been confirmed present (NatureServe. 2008).

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

References: (click for full references)

Bleeker, W. 2003. Hybridization and Rorippa austriaca (Brassicaceae) invasion in Germany. Molecular Ecology, 12: 1831-1841.  

Dorn, R.D. 1984. Vascular plants of Montana. Mountain West Publishers, Cheyenne.  

Elmore, C. 1998. New weed in California: creeping field cress. IPM Notes, 3(2): unpaginated.  

Elmore, C.L., L. Kuhns and T. Harpster.  1996.  Rorippa sylvestris, creeping fieldcress: A threat to production ornamentals and its control.  Hort Science 31(4)578.

Eilers, L.J., and D.M. Roosa. 1991. The vascular plants of Iowa. University of Iowa Press, Iowa City.

Mills, E.L., M.D. Scheuerell, J.T. Carlton, and D.L. Strayer. 1997. Biological invasions in the Hudson River basin. New York State Museum Circular, 57: 1-51.  

NC State.  2012.  Yellow fieldcress.  Accessed 12/9/13.  http://www.cals.ncsu.edu/plantbiology/ncsc/containerWeeds/Rorippa_sylvestris.htm

Stuckey, R.L. 1972. Taxonomy and distribution of the genus Rorippa (Cruciferae) in North America. Sida 4(4): 79-430.  

Thomas, R.D., and C.M. Allen. 1997. Atlas of the vascular flora of Louisiana, vols. 1-3 (Plus updates). Louisiana Department of Wildlife and Fisheries. Natural Heritage Program, Baton Rouge.  

Woldendorp, G., and M. Bomford. 2004. Weed eradication. Strategies, timeframes and costs. BRS Publication Sales, Common wealth of Australia: Camberra ACT Australia. 30 pp.

Yamane, A., H. Nishimura, and J. Mizutani. 1992. Allelopathy of yellow fieldcress (Rorippa sylvestris): Identification and characterization of phytotoxic constituents. Journal of Chemical Ecology 18(5):683-691.

Other Resources:

NatureServe. 2008. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.0. NatureServe, Arlington, Virginia. Available http://www.natureserve.org/explorer. (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: http://plants.usda.gov.  

Missouri Flora Web. http://www.missouriplants.com/Yellowalt/Rorippa_sylvestris_page.html  
http://www.invasive.org/browse/subject.cfm?sub=6330

http://www.illinoiswildflowers.info/weeds/plants/creeping_cress.htm

Author: Cao, L., and R. Sturtevant

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.