Najas marina
Najas marina
(spiny waternymph)
Native Transplant
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Najas marina L.

Common name: spiny waternymph

Synonyms and Other Names: Najas gracilis (Morong) Small, Najas major All., Najas marina var. recurvata DudleyNajas major var. angustifolia A. Braun ex K. Schum, spiny water nypmh, spiny-leaf naiad alkaline water-nymph, holly-leaf naiad, holly-leaved water nymph, large naias, saw tooth, marine naiad, marine water nymph, 



Taxonomy: available through www.itis.govITIS logo

Identification: Najas marina is a submersed plant with brittle stems that are often branched toward the upward portion of the plant. Stems branch distally, 6-45 cm ´ 0.5-4 mm.  The internodes (0.3-11cm) of the stem usually have conspicuous, brownish, prickly teeth. The leaves are opposite or sometimes in whorls of three, 0.5 to 4.0 cm long and 0.4-4.5mm wide, and have 8-13 triangular (multicellular) teeth along the leaf margins and prickles along the midrib on the underside of the leaf.  Leaf apex acute, with 1 tooth,.  Leaves spreading to ascending with age and stiff in age.  Sheaths 2--4.4 mm wide.

Plants are dioecious with the male and female flowers borne on separate individuals. The flowers are solitary in the leaf axils. The female flowers produce ovoid seeds 2.0 to 4.5 mm long that have 3 to 4-angled areolae that are irregularly arranged (

Flowers 1 per axil, staminate and pistillate on different plants. Staminate flowers in distal to proximal axils, 1.7-3 mm; involucral beaks 2-lobed, 0.3-0.7 mm; anthers 4-loculed, 1.7-3 mm. Pistillate flowers in distal to proximal axils, 2.5-5.7 mm; styles 1.2-1.7 mm; stigmas 3-lobed. Seeds not recurved, reddish brown, ovoid, 2.2-4.5 ´ 1.2-2.2 mm, apex with style situated at center; testa dull, 10-15 cell layers thick, pitted; areoles irregularly arranged, not in distinctive rows, not ladderlike, 3-4-angled, longer than broad, end walls slightly raised. 2n = 12 (Europe).

With its prickly internodes and prickles along the abaxial surface of the leaves, Najas marina is the easiest of our Najas to recognize.

Size: Perennial growing to 0.5m.

Native Range: Najas marina is native to Caribbean Territories, California, Hawaii, continental US, and Eurasia

US auto-generated map Legend USGS Logo
Alaska auto-generated map
Hawaii auto-generated map
Caribbean auto-generated map
Puerto Rico &
Virgin Islands
Guam auto-generated map
Guam Saipan
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences: Although widely distributed in the United States, populations are clustered in widely ranging geographic areas including Britain, but absent from colder regions.

Great Lakes Region: 1st Great Lakes sighting 1864 in the Lake Ontario drainage.  Established throughout the Great Lakes region (IL, IN, MI, MN, NY, OH, PA, WI).

Other US regions: Established in AZ, CA, FL, ND, NV, SD, TX, UT.

Ecology: Spiny naiad is found in 3' or more deep water in brackish or highly alkaline ponds, lakes, and coastal and inland marshes at elevations up to 1000 m in United States (Calflora Plant Observation Library).

Plants are reported to reproduce by seed and fragmentation (Tarver et al. 1986). Studies by Vierssen (1982) have shown seed germination of N. marina to be best in decomposing organic matter, at 24° C under dark conditions. It is in flower from September to November, and the seeds ripen from September to November. The plant prefers light (sandy), medium (loamy) and heavy (clay) soils. The plant prefers acid, neutral and basic (alkaline) soils and can grow in saline soil. It can grow in semi-shade (light woodland) or no shade.

Means of Introduction: Introduced via solid ballast

Agami and Waisel (1986) found the germination of N. marina to be increased after passing through the digestive tract of mallard ducks and postulate that ducks may be a major factor in long range dispersal of N. marina.

Status: Found in L. Ontario; widespread (U.S.EPA 2008).

Impact of Introduction: Najas marina can sometimes interfere with boating and fishing. It poses a realistic nuisance threat to ecosystems (U.S.EPA 2008). However, the plant is considered to be an excellent waterfowl food (Tarver et al. 1986).

References: (click for full references)

Agami, M. and Y. Waisel. 1986. The role of mallard ducks (Anas platyrhynchos) in distribution and germination of seeds of the submersed hydrophyte Najas marina. Oecologia (Berlin) 68: 473-475.

Agami, M. and Y. Waisel. 1988. The role of fish in distribution and germination of seeds of the submerged macrophytes Najas marina L. and Ruppia maritima L. Oecologia 76(1): 83—88.

Flora of North America.  2008.

Haynes, R. R. 1979. Revision of North and Central American Najas (Najadaceae). Sida 8: 34-56.

Lembi, C. A. 2003. Aquatic Plant Management. Purdue University Cooperative Extension Service. 20 pp.

Minnesota Department of Natural Resources (MN DNR). 2013. Najas marina  L.: Sea Naiad. Available Accessed 23 April 2013.

Stuckey, R. L. 1985. Distributional history of Najas marina (spiny naiad) in North America. Bartonia 51: 2--16.

Tarver, D. P., J. A. Rogers, M. J. Mahler, and R. L. Lazor. 1986. Aquatic and Wetland Plants of Florida. Third Edition. Florida Department of Natural Resources, Tallahassee, Florida.

Triest, L., J. van Geyt, and V. Ranson. 1986. Isozyme polymorphism in several populations of Najas marina L. Aquatic Bot. 24: 373--384.

U.S. EPA (Environmental Protection Agency). (2008) Predicting future introductions of nonindigenous species to the Great Lakes. National Center for Environmental Assessment, Washington, DC; EPA/600/R-08/066F. Available from the National Technical Information Service, Springfield, VA, and

Vierssen, V. W. 1982. Some notes on the germination of seeds of Najas marina. Aquatic Botany 12: 201-203.

Viinikka, Y. 1973. The occurrence of B chromosomes and their effect on meiosis in Najas marina. Hereditas (Lund) 75: 207--212.

Wentz, W. A. and R. L. Stuckey. 1971. The changing distribution of the genus Najas (Najadaceae) in Ohio. The Ohio Journal of Science 7(15): 292—302.

Other Resources:

Author: Cao, L, and L. Berent

Revision Date: 4/22/2014

Citation Information:
Cao, L, and L. Berent, 2018, Najas marina L.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL,, Revision Date: 4/22/2014, Access Date: 1/24/2018

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.

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Citation information: U.S. Geological Survey. [2018]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [1/24/2018].

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