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

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).

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).

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

Environmental	Socioeconomic	Beneficial

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).

Potential:
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.
Realized:
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).

Potential:
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.
Potential:
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).

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.

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

Physical
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).

Chemical
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.