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Montana Field Guide

Montana Field Guides

Blunt-leaved Pondweed - Potamogeton obtusifolius

Species of Concern
Native Species

Global Rank: G5
State Rank: S3
(see State Rank Reason below)

Agency Status
MNPS Threat Rank: 2
C-value: 8

External Links

State Rank Reason (see State Rank above)
Known from over a dozen occurrences in northwest Montana. Several contain moderate to large-size populations and occur in valley and foothill locations in a variety of federal, state, and private ownerships. A few populations are on lands managed specifically for their conservation value. Some populations are vulnerable to impacts associated with development, recreation and increased sediment and nutrient loads.
General Description
Blunt-leaved Pondweed is an aquatic, rhizomatous perennial with slender, submergent, or floating stems that are up to 100 cm long. The leaves are linear, 3-10 cm long, and 2-4 mm wide, each with a small round gland on either side at the base. There is a white-membranous leaf stipule that surrounds the stem above the point where the leaf diverges. Herbage is glabrous. The minute flowers are borne on long-stalked, narrow, interrupted spikes in the axils of the upper leaves. The flowers consist only of the stamens and an ovary; there are no petals or sepals. The achene is oval in outline, 3-4 mm long, and compressed with a keel on the outer edge.

Mature fruit in late July-August.

Diagnostic Characteristics
This species is distinguished from other narrow-leaved Potamogeton species by a combination of the membranous rather than fibrillous stipules, presence of the pair of glands at the base of leaves, and achene dimensions. The narrow-leaved pondweeds are a very difficult group to distinguish; a technical key must be employed.

Species Range
Montana Range


Range Comments
Circumboreal south to WA, WY and NY (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 22

(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)

Shallow water of lakes, ponds, and sloughs in the valley, foothill, and montane zones.
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

  • Additional ReferencesLegend:   View Online Publication
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    • Aulio, K. and M. Salin. 1982. Enrichment of copper, zinc, manganese, and iron in five species of pondweeds (Potamogeton spp.). Bulletin of Environmental Contamination and Toxicology 29:320-325.
    • Danell, K. 1977. Short-term plant successions following the colonization of a northern Swedish lake by the muskrat, Ondatra zibethica. Journal of Applied Ecology 14:933-947.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • Pip, E. 1987. The ecology of Potamogeton species in central North America. Hydrobiologia 153:203-216.
    • Toivonen, H. and C. Nybom. 1989. Aquatic vegetation and its recent succession in the waterfowl wetland Koijarvi, S. Finland. Ann. Bot. Fennici 26:1-14.
    • Toivonen, H. and S. Back. 1989. Changes in aquatic vegetation of a small eutrophicated and lowered lake (southern Finland). Ann. Bot. Fennici 26:27-38.
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Citation for data on this website:
Blunt-leaved Pondweed — Potamogeton obtusifolius.  Montana Field Guide.  .  Retrieved on , from