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| NAS - Nonindigenous Aquatic Species |
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Common Name: water cress
Taxonomy: available through 
Identification: Water cress is a fast-growing, aquatic or semi-aquatic, perennial herb. Floating or prostrate in mud. Stems succulent, hollow, and much branched, 1 to many, 4–25 in. long, rooting at nodes. Leaves pinnately divided; leaflets 3–7, oval to egg-shaped, entire to wavy-edged. Flowers small (6 mm, diameter) in terminal clusters, white. Sepals, erect, green, about 3 mm long; petals white, about 4 mm long and 4 long stamens attached near their bases to the filaments. Ovary about 3 mm long, style short, stigma with two lobes. Fruits borne on spreading pedicels and slightly curved upward. The double row of seeds in each half of the siliqua is a well marked character. The valves of the ripe siliqua beaded; seeds suborbicular and compressed, with 25 alveoli on each side of the testa. It can grow to a height of 50-200 cm, with a stem up to 20 mm in diameter and with leaves up to 27 cm in length.
Size: to 200cm
Native Range:
Eurasia & Asia
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 Alaska |
Hawaii |
Caribbean |
Interactive maps: Continental US, Alaska, Hawaii, Caribbean
Nonindigenous Occurrences:
Water cress is usually considered as introduced in America, S. Africa, Australia and New Zealand. It was first introduced in United States in 1831. Now recorded in the following states: AK, AL, AR, AZ, CA, CO, CT, DC, FL, GA, IA, ID, IL, IN, KS, KY, LA, MA, ME, MI, MN, MO, MS, MT, NC, NE, NH, NJ, NM, NV, NY, OH, OK, OR, PA, RI, SC, SD, TN, TX, UT, VA, VT, WA, WI, WV, WY.
1st Great Lakes sighting 1847 Lake Ontario
Ecology: Well-suited to water that is slightly alkaline. Water cress grows at the edges of slow-flowing water in lakes, reservoirs, streams, rivers, either just below or above water level. The depth of water in commercial watercress beds is about 3-6 in. It is usually absent from stagnant water. Watercress appears to be intolerant of heavy shade. A relatively high humidity is required for optimum growth. It is mainly a lowland species but is said to extend up to 6500 ft. Flowering time: March to October. Grows throughout winter, continually occupying surface space in SW Wisconsin. Most abundant in summer and autumn.
Means of Introduction: Intentionally introduced by green industry and cultivation. Fragments are dispersed unintentionally by wind, water, and animal
Status: Established. Naturalized throughout North America, north to Alaska
Impact of Introduction:
Water cress may be a noxious weed or invasive. In arid regions of western states, it can alter function and block streams. It was reported to block water flow in springs in South Central Wisconsin. Extracts can attract schistosomiasis host Biomphalaria glabrata (snail).
Rich source of potential anticarcinogen; Edible green used in salads, cooking; Homeopathic properties; Wastewater treatment. “Watercress contains significant amounts of iron, calcium and folic acid, in addition to vitamins A and C. Many benefits from eating watercress are claimed, such as that it acts as a mild stimulant, a source of phytochemicals and antioxidants, a diuretic, an expectorant, and a digestive aid. It also appears to have cancer-suppressing properties. It is widely believed to help defend against lung cancer.” (http://en.wikipedia.org/wiki/Watercress)
Remarks: Synonyms: Nasturtium officinale var. silifolium; Sisymbrium nasturtium-aquaticum L.; Nasturtium nasturtium-aquaticum.; recently Rorippa nasturtium-aquaticum
References
Howard, H.W., Lyon, A.G. 1952. Nasturtium Officinale R. Br. (Rorippa Nasturtium-Aquaticum (L.) Hayek). The Journal of Ecology 40 (1): 228-245.
Redding, T.S., Midlen, A. 1997. The treatment of aquaculture wastewaters - A botanical approach. Journal of Environmental Management 50 (3): 283-299.
Tardio, M Pardo-De-Santayana, Morales, R. 2006. Ethnobotanical review of wild edible plants in Spain. Botanical Journal of the Linnean Society 152 (1): 27-71.
Tenorio, R.C., Drezner, T.D. 2006. Native and invasive vegetation of karst springs in Wisconsin's Driftless area. Hydrobiologia 568: 499-505.
Other Resources:
GLIFWC-Maps
The PLANTS Database 2008. National Plant Data Center, NRCS, USDA. Baton Rouge, LA 70874-4490 USA.http://plants.usda.gov/
Connecticut Botanical Society. http://ct-botanical-society.org/galleries/rorippanast.html
http://en.wikipedia.org/wiki/Watercress
www.calflora.org
http://dnr.wi.gov/invasives/classification/pdfs/LR_Nasturtium_officinale.pdf
http://www.pnwflowers.com/flower/rorippa-nasturtium-aquaticum
Author: Ling Cao
Contributing Agencies: 
NOAA - GLERL
Revision Date: 7/25/2008 Citation for this information:
Ling Cao. 2009. Nasturtium officinale. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=2737> Revision Date: 7/25/2008
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