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Montana Field Guide

Montana Field Guides

Beck Water-marigold - Bidens beckii
Other Names:  Megalodonta beckii

Species of Concern
Native Species

Global Rank: G5
State Rank: S2
(see State Rank Reason below)

Agency Status
MNPS Threat Rank: 3
C-value: 8

External Links

State Rank Reason (see State Rank above)
Known from ten occurrences in the western valleys of the state, including 6 moderate to large populations and one historical occurrence from Salmon Lake dating to 1937. However, the species may be more abundant in the state than what current data suggests. Threats and impacts to populations in Montana include boating activity, lake shore development, aquatic weeds and use of aquatic herbicides.
General Description
Beck Water-marigold is an aquatic perennial herb with lower stems that are submerged and upper portions usually emergent. Submerged leaves are opposite, sessile, and divided into numerous thread-like segments. The lance-shaped, emergent leaves are sessile, opposite, and 2-4 cm long with sharply toothed margins. Solitary flower heads are borne on the ends of the emergent stems. Each head has 2 series of involucral bracts, with the outer being larger and leafier than the inner bracts. The yellow rays are 1-2 cm long, and the disk flowers are also yellow. Achenes are 10-14 mm long and nearly round in cross-section, with 3-6 long, slender, barbed awns at the tops.

Flowering in late August-September.

Diagnostic Characteristics
Bidens beckii is the only truly aquatic member of the Asteraceae in our area. It is readily distinguished by its aster-like flowers and dimorphic emergent and submergent leaves.

Species Range
Montana Range


Range Comments
BC to QC south to OR, MT, MO, PA and NY (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 165

(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)

Still or slow-moving water of lakes, rivers, and sloughs in the valleys, 0.1-3 m deep.

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

The following animal species have been reported as pollinators of this species or genera where their geographic ranges overlap: Bombus griseocollis and Bombus impatiens (Plath 1934, Colla and Dumesh 2010).

  • Literature Cited AboveLegend:   View Online Publication
    • Colla, S.R. and S. Dumesh. 2010. The bumble bees of southern Ontario: notes on natural history and distribution. Journal of the Entomological Society of Ontario 141: 39-68.
    • Plath, O.E. 1934. Bumblebees and their ways. New York, NY: Macmillan Company. 201 p.
  • Additional ReferencesLegend:   View Online Publication
    Do you know of a citation we're missing?
    • Bier, Charles.
    • Bissell, J.K. & C.W. Bier. 1987 Dec 30. Presque Isle State Park: Botanical Survey and Natural Community Classification. U87BIS02.
    • Fairbrothers, D.E. et al. 1965. Aquatic Vegetation of New Jersey. Rutgers Univ. Ext. Serv. College of Agriculture. Ext. Bull. 382. Camden, New Jersey, USA. B65FAI01PAUS.
    • Fernald, M. L. 1950. Gray's manual of botany. Eighth edition. A handbook of the flowering plants and ferns of the central and northeastern United States and Adjacent Canada. American Book Co., New York.
    • Gleason, H.A. 1952. New Britton & Brown. Illustrated Flora. Lancaster Press Inc. Lancaster, Pa. B52GLE01PAUS
    • Greene, E.L. 1901. Studies in the Compositae - VIII. Pittonia 4:242-284. A01GRE01PAUS
    • Hartman, R.T. 1986 July-Aug. Field survey at Conneaut Lake, Crawford County, for Megalodonta Beckii.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
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Citation for data on this website:
Beck Water-marigold — Bidens beckii.  Montana Field Guide.  .  Retrieved on , from