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Montana Field Guide

Montana Field Guides

Slender Naiad - Najas flexilis

Native Species

Global Rank: G5
State Rank: S4
C-value: 7

Agency Status


External Links

General Description
Stems 5–40 cm. Leaves 10–35 mm long; the dilated base 2–3 mm wide. Female flowers 2–5 mm long. Achenes ca. 3 mm long; seeds smooth, shiny, sometimes minutely spotted (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Diagnostic Characteristics
Slender Naiad - Najas flexilis, Native
*Leaves: 10–35 mm long with a dilated base that is 2–3 mm wide. From about their mid-section, leaves have a long taper that terminates in a long slender point. Prickles lacking.
*Seeds: Smooth, shiny, and sometimes minutely spotted.

Guadalupe Water-nymph - Najas guadalupensis, SOC
*Leaves: 5-15 mm long with minutely toothed margins. Ribbon-like with short tapering tips and expanded bases. Additional leaves are often found in the axils. Prickles lacking.
*Seeds: Dull and coarsely pitted, with a honeycomb surface.

Spiny NaiadNajas marina, Exotic
*Leaves: Coarsely serrated margins with 8 to 13 teeth on each side of the blade. Prickles can be found on the abaxial (lower) surface of the blade.
*Seeds: Ovoid, reddish brown, and pitted with areoles (outer two coatings of the testa) irregularly arranged, not in distinctive rows or not ladder-like. Seeds are longer than broad with the end walls slightly raised.

Brittleleaf Naiad - Najas minor, NOT DOCUMENTED IN MONTANA
*Leaves: At maturity, blades recurve and become stiff with age. Prickles lacking.
*Seeds: Broader than long and with areoles arranged in longitudinal rows – like the rungs of a ladder.

The Najas genus is sometimes placed in the Family Hydrocharitaceae, also known as the Waterweed or Frog’s-bit Family.

Species Range
Montana Range Range Descriptions


Range Comments
BC to NL south to CA, NV, KY and VA (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 479

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density



(Observations spanning multiple months or years are excluded from time charts)

Usually shallow, often alkaline water of lakes, sloughs; valleys (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

  • Literature Cited AboveLegend:   View Online Publication
    • eFloras. No Date. Published on the Internet Missouri Botanical Garden Herbarium, St. Louis, Missouri and Harvard University Herbarium, Cambridge, Massachusetts
    • Flora of North America Editorial Committee (FNA). 2000. Flora of North America north of Mexico. Vol. 22. Magnoliophyta: Alismatidae, Arecidae, Commelinidae (in part), and Zingiberidae. Oxford Univ. Press, New York. xxiii + 352 pp.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2022. Manual of Montana Vascular Plants, Second Edition. Fort Worth, TX: BRIT Press. viii + 779 p.
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Citation for data on this website:
Slender Naiad — Najas flexilis.  Montana Field Guide.  .  Retrieved on , from