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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.

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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

Taxonomy: available through www.itis.gov

Identification:

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).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

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

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.

Impact of Introduction:

Summary of species impacts derived from literature review. Click on an icon to find out more...

Ecological	Economic	Other

Najas minor can form dense, monospecific stands in shallow water that inhibit the growth of native species of aquatic macrophytes and hinder swimming, fishing, boating, and other forms of water contact recreation (U.S. EPA 2008). However, Capers et al. (2007) found that Najas minor was less likely to be present when native plant diversity was high, and Trebitz and Taylor (2007) found no evidence of dominance by Najas minor.

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.

References: (click for full references)

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Other Resources:
Maine Volunteer Lake Monitoring Program

 

US Fish and Wildlife Service Ecological Risk Screening Summary for Najas minor

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

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.