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Montana Field Guides

Columbia Water-meal - Wolffia columbiana

Species of Concern
Native Species

Global Rank: G5
State Rank: S2S3
(see State Rank Reason below)
State Threat Score: No Known Threats
C-value: 7

Agency Status


External Links

State Rank Reason (see State Rank above)
Rare. Known from several water bodies in the valleys of western Montana. Additional information on the species is needed within Montana to more precisely determine the species' conservation status.
General Description
Columbia Water-meal, a minute floating aquatic perennial, is among the world's smallest flowering plants. The plant body is rootless and thalloid, with no distinction between stem and leaf. The symmetrical, globular, uniformly green thalli are less than 1.5 mm long, smooth and rounded on the back, and floating just below the surface of the water. The plants rarely flower and for the most part reproduce vegetatively by budding. They often grow in large colonies.

Rarely if ever observed flowering; vegetative material observed July-September.

Diagnostic Characteristics
Montana species of the Duckweed Family are all small, perennial, free-floating, aquatic herbs. In this family the term "leaf" cannot be used because a leaf consists of a stem (petiole) and a blade (Landolt in FNA 2000). Instead the term "frond" is used. Be aware that species can grow in the same place naturally.

Lemna - Duckweed, native
* Fronds: Green above and mostly below.
* Root: 1 per frond, sometimes absent.
* Veins: 1-3 per frond.

Spirodela - Duck-meal, native
* Fronds: Green above and usually purplish below.
* Roots: 2 or more per frond
* Veins: 3 or more per frond.

Wolffia - Water-meal, native
* Fronds: Green to brown; round.
* Root: 0; absent.
* Veins: 0; absent.

Wolffia columbiana is distinguished from other Wolffia by the upper surface of its thallus, which is rounded and smooth (sometimes with minute humps) rather than flattened and/or with sunken brown dots.

Species Range
Montana Range Range Descriptions


Range Comments
Throughout most of North America, south to S. America. Sparse.

Observations in Montana Natural Heritage Program Database
Number of Observations: 17

(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)

Fresh, shallow water of ponds and sloughs in the valley zone.
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

Ecological Systems Associated with this Species
  • Commonly Associated with these Ecological Systems
    Wetland and Riparian Systems

Threats or Limiting Factors
Threat impact not assigned because threats are not known (MTNHP Threat Assessment 2021).

  • Additional ReferencesLegend:   View Online Publication
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    • Bernard, F.A. and J. M. Bernard. 1990. Flower structure and life history of Wolffia australiana (Benth.) den Hartog & van der Plas. Bulletin of the Torrey Botanical Club 117(1):18-26.
    • Burk, C. J., S. D. Lauermann, and A. L. Mesrobian. 1976. The spread of several introduced or recently invading aquatics in western Massachusetts. Rhodora 78(816):767-772.
    • Butler, D. R. 1976. Dendrogeomorphic and biogeographic studies of snow avalanche slopes, Glacier National Park. Proceedings of the Nebraska Academy of Science Affiliated Society 86:71-72.
    • Cassani, J. R. 1981. Feeding Behaviour of Underyearling Hybrids of the Grass Carp, Ctenopharyngodon idella and the bighead, Hypophthalmicthys nobilis on Selected Species of Aquatic Plants. Journal of Fish Biology. 18:127-133.
    • Catling, P. M. and V. R. Brownell. 1987. New and significant vascular plant records for Manitoba. Canadian Field-Naturalist 101(3):437-439.
    • Cody, W.J. 1980. Wolffia columbiana (Lemnaceae), water-meal, new to Manitoba. Canadian Field-Naturalist 94(2):193-194.
    • Fassett, N. C. 1985. (3rd ed.) A Manual of Aquatic Plants, with Revision Appendix by E. C. Ogden. University of Wisconsin Press, Madison. 405 pp.
    • Kline, L. and B. McCune. 1987. Factors influencing the distribution of Wolffia columbiana and Wolffia punctata (Lemnaceae). Northwest Science 61:41-43.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • 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:
Columbia Water-meal — Wolffia columbiana.  Montana Field Guide.  .  Retrieved on , from