Najas minor All.

Common Name: Brittle waternymph

Synonyms and Other Names:

Caulinia minor (All.) Coss. & Germ., minor naiad, brittle water-nymph; brittle naiad, brittle-leaf naiad, European naiad, slender naiad, bushy naiad, lesser naiad

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Habit: Najas minor is an annual submersed rooted or floating plant (Haynes 1979).

Stem/Roots: Slender, branching stems and fibrous roots. Although its growth is usually compact and relatively bushy, the highly branched stems can grow up to 4 ft (1.2 m) in length and fragment easily (Haynes 1979).

Leaves: Opposite (paired), sometimes appearing whorled, and usually bunched at leaf axils. The leaves are typically stiff, curled and pointed, and have spines along the margins that are visible to the naked eye, if not a hand lens. Leaves are about 1 mm wide and 0.5 to 3.5 cm long (Haynes 1979).

Flowers: Reduced, imperfect flowers 1-2 per axil, with separate male and female flowers on the same plant (monoecious) (Haynes 1979).

Fruit/Seeds: Slightly recurved, purplish, fusiform seeds with tiny pits wider than long around the girth (Haynes 1979).

Look-alikes: Other naiads (Najas spp.). Najas minor, with its mature leaves recurved, and its seed pits (areolae) arranged in longitudinal rows like the rungs of a ladder, is one of the more distinctive species of Najas (Meriläinen 1968). Proper identification without reproductive structures requires genetic testing due to morphological similarities to N. gracillima and N. marina (Les et al. 2015).

Size: up to 1.2 m in length (Haynes 1979)

Native Range: Najas minor is native to Europe, western Asia, and northern Africa (Meriläinen 1968; Triest 1988).

Great Lakes Nonindigenous Occurrences: This species has been recorded in Illinois, Indiana, Michigan, Minnesota, New York, Ohio, Pennsylvania and Wisconsin.

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 Najas minor are found here.

Full list of USGS occurrences

State/ProvinceFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IL200120011Little Calumet-Galien
MI194920227Clinton; Detroit; Huron; Kalamazoo; Lake Huron; Ottawa-Stony; Upper Grand
NY1935202014Chautauqua-Conneaut; Grass; Great Lakes Region; Irondequoit-Ninemile; Lake Champlain; Lake Ontario; Lower Genesee; Mettawee River; Oak Orchard-Twelvemile; Oneida; Oswego; Salmon-Sandy; Seneca; Upper Genesee
OH1932202214Ashtabula-Chagrin; Auglaize; Black-Rocky; Cedar-Portage; Cuyahoga; Grand; Huron-Vermilion; Lake Erie; Lower Maumee; Sandusky; Southern Lake Erie; St. Joseph; Tiffin; Western Lake Erie
PA198720222Chautauqua-Conneaut; Lake Erie
VT196019651Lake Champlain
WI200920173Lake Michigan; Upper Fox; Wolf

Table last updated 11/29/2022

† Populations may not be currently present.

* HUCs are not listed for areas where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: Najas minor prefers stagnant or slow-moving waters, such as ponds, lakes, reservoirs, canals and is capable of growing in depths up to four meters (Meriläinen 1968). It is more tolerant of turbidity and eutrophic conditions than some of the native species of Najas and has replaced them in many instances (Wentz and Stuckey 1971).

Najas minor is water-pollinated (Triest 1988). Although this annual can reproduce by fragmentation, the primary means of reproduction appears to be by one-seeded fruits (Meriläinen 1968).

Populations of Najas spp. within reservoirs can fluctuate dramatically over a period of a few years and have been correlated with years of low rainfall and increased amounts of available light (Peltier and Welch 1970).

Means of Introduction: The vector of introduction of N. minor to North America is not clear. It could have been accidentally introduced with more commonly cultivated species, such as rice (McIntyre and Barrett 1985; Les and Mehrhoff 1999). Alternatively, it could have been introduced to the Great Lakes, the Hudson River, or upper Chesapeake Bay by shipping (Mills et al. 1993; Mills et al. 1997).

Najas minor spreads through its many small seeds, which may be carried by waterfowl (Meriläinen 1968; Agami and Waisel 1986), and can easily hitchhike to other water bodies on boats and boat trailers (Tarver et al. 1986).

Status: Established in all previously mentioned state occurrences.

Great Lakes Impacts: Najas minor has a moderate environmental impact in the Great Lakes.
Brittle waternymph starts growing early in the season, which often leads to the block the sunlight from reaching native species and inhibiting their growth (Ohio EPA 2001, Robinson 2004). This species can also out-compete nearby plants for space (Office of Water Resources 2010).

Najas minor grows aggressively in shallow waters and has formed dense, monospecific stands in the shallow waters of Lake Erie (U.S. EPA 2008). Najas minor can also form dense underwater meshes with other exotic species such as Hydrilla verticillata (Kay and Hoyle 1999). These dense plant communities can produce unfavorable conditions for to fish and waterfowl (Kay and Hoyle 1999, Office of Water Resources 2010).

Animals may also be driven out of N. minor dominated ecosystems if they are dependent on the displaced native vegetation for survival (Robinson 2004).

Although, this species typically invades shallow water, in North Carolina dense shoals of N. minor have grown in waters up to 4 meters deep (Kay and Hoyle 1999). Dense populations of brittle waternymph have increased sedimentation rates and clogged waterways in Massachusetts (Robinson 2004).

As dense mats of brittle waternymph die and decompose, the amount of oxygen in nearby water and sediment maybe be significantly decreased (Robinson 2004). In extreme cases, anoxic conditions can lead to fish kills (Robinson 2004).

Najas minor has a moderate socio-economic impact in the Great Lakes.
Najas minor populations can reduce the discharge capacity (quantity of water) of channels (WI DNR 2010).

Dense stands of N. minor can hinder recreational activities such as, boating, fishing, and/or swimming (Office of Water Resources 2010, U.S. EPA 2008, WI DNR 2010). Along with reduced recreational ability, populations of brittle waternymph can also diminish the aesthetic value of the surrounding areas (WI DNR 2010).

Limited recreational use and a decline in aesthetic value associated with large N. minor infestations can lead to reduced property values around the effected waterbody (Robinson 2004).

Current research on the beneficial effects of Najas minor in the Great Lakes is inadequate to support proper assessment.
Mallard ducks and 18 other types of waterfowl eat the seeds of many Najas spp. (Agami and Waisel 1986, Tarver et al. 1986).

Najas minor is tolerant of adverse growing conditions including increased turbidity, eutrophic ecosystems, and some pollution (Wentz and Stuckey 1971, WI DNR 2010).

Management: Regulations (pertaining to the Great Lakes)
Najas minor is prohibited in Minnesota, Wisconsin, and Illinois (GLPANS 2008).  In Minnesota it is illegal to possess, import, purchase, sell, propagate, transport, or introduce N. minor or any related varieties or hybrids (Invasive Species Program 2011). The New York Invasive Species Council ranks this species moderate ecological risk and recommends that the species be regulated (New York Invasive 2010).

The Great Lakes Indian Fish & Wildlife Commission ranked this species as a “low priority” for control in 2011, because it was not detected in their ceded territories (Falck et al. 2012).

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

There are no known biological control methods for this species (Ohio EPA 2001).

Manual removal may provide short-term relief by reducing the biomass of N. najas, however, small plant fragments may break off and create new plants/infestations (Office of Water Resources 2010, Ohio EPA 2001, Robinson 2004).

Benthic barriers (which restrict light and upward growth of submerged plants) may be effective in controlling N. minor in high traffic areas: boating lanes, docks, and swimming beaches (Robinson 2004). These structures need to be anchored to the sediment and regularly maintained, which may impact other benthic and/or plant organisms (Robinson 2004).

Herbicides may be most effective for controlling large populations of brittle waternymph (Office of Water Resources 2010). Herbicides containing amine salts of Endothall (Hydrothol 191®), dipotassium salt of Endothall (Aquathol K® Liquid, Aquathol Super K® granular), Diquat dibromide (Reward®), or Fluridone (Sonar®, Avast!®) will control N. minor (Robinson 2004, Water Bureau 2005). Cutrine®, Komeen®, Nautique®, and Weedtrine®, will also provide effective control of brittle waternymph (Robinson 2004, Water Bureau 2005).

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

Remarks: Seven other species of Najas are reported by Haynes (1979) as occurring in the United States. Because several of the species are morphologically similar, identification of the various species can sometimes be difficult. Najas minor is easily confused with the other Najas species, slender water nymph (N. flexilis), common water nymph (N. guadalupensis) and northern naiad (N. gracillima). These species can be differentiated from N. minor by looking at the leaf bases and seeds.

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Author: Pfingsten, I.A., L. Cao, and L. Berent

Contributing Agencies:

Revision Date: 8/19/2019

Citation for this information:
Pfingsten, I.A., L. Cao, and L. Berent, 2022, Najas minor All.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 8/19/2019, Access Date: 12/1/2022

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.