Taxonomic name: Najas minor All.
Synonyms: Caulinia minor (All) Coss. & Germ.
Common names: brittle naiad (English), brittle waternymph (English), European naiad (English), minor naiad (English), slender naiad (English), slender-leaved naiad (English), spiny-leaf naiad (English)
Organism type: aquatic plant
Najas minor is a submerged aquatic herb native to Europe and Asia that has established in eastern United States and Ontario. Initially recorded in the 1930s, it has established populations in 26 states in the US. It creates dense, monospecific stands that may displace native aquatic plants and reduce the recreational and aesthetic value of lakes, ponds, and rivers.
Najas minor is a submersed, annual, aquatic herb. Its growth is usually compact and relatively bushy. The stems may reach up to 2.5 m long and are profusely branched near their apex. Leaves are opposite or subopposite, about 1 mm wide and 0.5 to 3.5 cm long, becoming stiff and recurved with age. Leaves have 7 to 15 small, but conspicuous teeth along each side of the leaf. Sheaths at the base of the leaf are truncate to auriculate, with fine teeth along the upper margin. Flowers are small, inconspicuous, and borne in the leaf axils on the same plant. Fruits are single seeded but abundantly produced. Fruits are 1.5 to 3.0 mm long and slightly curved with rectangular areolae arranged in distinct longitudinal rows. (EL-ERDC, 2007; Cao, 2010).
Ceratophyllum spp., Najas flexilis, Najas gracillima, Najas guadalupensis
lakes, water courses
Najas minor prefers calm waters such as ponds, lakes, and reservoirs but may grow in streams and rivers as well. It prefers alkaline environments and is known to inhabit pH levels of 6.0-9.3 with an optimum range of about 6.6-7.2. It occurs of depths of up to 5 m with an ideal optimum of about 0.5-2 m and temperatures down to 8°C. It may inhabit brackish waters with a salinity of up to 0.3 ppt. N. minor is tolerant to turbidity and eutrophic conditions, which may allow it to out compete and replace native species (DNR, 2007; Wentz & Stuckey, 1971; Robinson, 2004)
Najas minor establishes dense monocultures that may exclude other native aquatic plants and replaces native Najas species. Unlike some of the other invasive aquatic plants N. minor does not produce long stems that spread on the surface of the water; it grows very densely under the surface producing shoots upto a meter long that shade out other plants and interfere with recreational activity such as swimming, boating, and fishing and reduce the aesthetic value of waters. It is also believed to induce conditions that are adverse to fish and waterfowl. N. minor may reduce the discharge capacity of channels as well. Its negative effects are typically amplified in enriched, low-energy systems (DNR, 2007; Hellquist & Straub, 2002; Cao, 2010; Capers et al, 2005).
Najas minor is a preferred food source for waterfowl who readily consume its abundant seed supply (DNR, 2007).
Native range: Austria, Belgium, Bulgaria, Czech Republic, France, Germany, Hungary, Italy, Poland, Portugal, Romania, Russian Federation, Serbia and Montenegro, Ukraine, Morocco, India, Turkey, Japan
Known introduced range: eastern United States, Ontario
Introduction pathways to new locations
Landscape/fauna "improvement": Intentional propagation of Najas spp. as a food source for waterfowl was widely advocated in the 1930s (Les & Merhoff, 1999; DNR, 2007).
Pet/aquarium trade: Najas minor may be introduced through disposal of aquarium species (DNR, 2007).
Road vehicles (long distance): Najas minor or its seeds may cling to boat hulls or boat trailers in inconspicuous places and be transported to other locations where they can establish (Capers et al, 2005).
Ship/boat hull fouling: Najas minor or its seeds may cling to boat hulls or boat trailers in inconspicuous places and be transported to other locations where they can establish (Capers et al, 2005).
Local dispersal methods
Consumption/excretion: Waterfowl consume seeds of Najas minor and excrete them in new locations. This method is believed to be a primary means of long distance dispersal (Capers et al, 2005; Les & Mehrhoff, 1999).
Translocation of machinery/equipment (local): Najas minor or its seeds may cling to boat hulls or boat trailers in inconspicuous places and be transported to other locations where they can establish (Capers et al, 2005).
Water currents: Water or wind currents may transport fragments of Najas minor to establish in other locations (EL-EDRC, 2007).
Wind dispersed: Water or wind currents may transport fragments of Najas minor to establish in other locations (EL-EDRC, 2007).
Preventative measures: Najas minor is reported as noxious and is regulated in Alabama, Connecticut, Maine, Massachusetts, New Hampshire, South Carolina, Washington. It is illegal to possess, import, purchase, sell, propogate, transport, or introduce N. minor in Minnesota. N. minor was included on a Washington Department of Agriculture list of quarantined species in 2000, and it is illegal to sell, trade, or transport in the state of Washington. Education and population monitoring are recommended to help prevent its establishment (DNR, 2007; Hamel & Parsons, 2001).
Chemical: Small scale herbicide treatments of endothall, dipotassium, and endothall mono have been conducted in hopes to provide “nuisance relief.” However, it has been reported that some non-target plant species have been affected as well. The following herbicides and brands were reported to yield excellent control for N. minor by the US army Corp of Engineers: diquat: Reward, Weedtrine-D; fluridone: Sonar AS, Sonar SRP, Sonar PR, Sonar Q, and Avast!; and endothall Aquathol K, Aquathol Super K, Hydrothol 191. N. minor was found to be completely unaffected by the herbicide butachlor (DNR, 2007; EL-EDRC, undated; Chattopadhyay et al, 2006).
Mechanical: The use of aquatic plant harvesters, large boats that cut and remove vegetation, has been recommended as a means to remove large quantities of Najas minor. Similarly, rotovators, basically large underwater rototillers that remove aquatic plant tissue and root crowns, are another recommended mechanical control. The use of hand cutters may be effective for smaller populations (EL-ERDC, undated).
Najas minor reproduces sexually and asexually. Sexual production of an abundant seed supply and seed banks of up to tens of millions of seeds/ha appears to be its primary means of reproduction. It may also reproduce vegetatively producing clonal populations that may fragment and propogate (DNR, 2007; EL-EDRC, 2007)
The reproductive season of Najas minor starts in July, when flowers appear. Seed production peaks in September, and continues into October. During the late summer or early fall, the stems become brittle, and the profusely branched apical portions of the stem break into small fragments. Seeds remain attached in the leaf axils, and the fragments are dispersed by wind and water currents. Seed germination occurs in early spring to late summer (Cao, 2010; DNR, 2007).
Reviewed by: Robert S. Capers, plant collections manager, George Safford Torrey Herbarium, Department of Ecology and Evolutionary Biology, University of Connecticut
Principal sources: Department of Natural Resources (DNR), Wisconsin., 2007. Aquatic Plant Brittle/Lesser/Bushy/Slender/Spiny/Minor Naiad; Waternymph
Environmental Laboratory (EL) U.S. Army Engineer Research and Development Center (ERDC), 2007. Information Sheet: Najas minor L. (Spiny Naiad)
Ling Cao. 2010. Najas minor. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
Compiled by: National Biological Information Infrastructure (NBII) & IUCN/SSC Invasive Species Specialist Group (ISSG)
Last Modified: Friday, 4 January 2013