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Montana Field Guide

Montana Field Guides

Shining Flatsedge - Cyperus bipartitus
Other Names:  Cyperus rivularis

Species of Concern
Native Species

Global Rank: G5
State Rank: S1
(see State Rank Reason below)
State Threat Score: No Known Threats
C-value: 4

Agency Status


External Links

State Rank Reason (see State Rank above)
Rare in Montana, where it is currently known from only the Bitterroot Valley.
General Description
Caespitose annual. Stems ascending to erect, 2–8 cm. Leaves mainly basal, 0.5–2 mm wide, U-shaped in cross-section. Inflorescence of hemispheric spikes of subsessile spikelets. Spikelets compressed, 3–15 mm long. Scales purplish, 2–2.5 mm long with rounded, minutely apiculate tips and obscure veins. Flowers: stamens 2 or 3; style 2-branched. Achene obovate, black, ca. 1 mm long, 2-sided, apiculate (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Fruit mature in August-September.

Diagnostic Characteristics
Cyperus acuminatus, C. aristatus, and C. erythrorhizos all have scales with pointed or short, awn-tipped scales, unlike the blunt scale of C. rivularis.

Species Range
Montana Range Range Descriptions


Range Comments
Throughout temperate North America to S. America. Known from Ravalli County (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 7

(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)

Wet, often gravelly shores of rivers, lakes and ponds 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

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

  • Literature Cited AboveLegend:   View Online Publication
    • 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.
  • Web Search Engines for Articles on "Shining Flatsedge"
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Citation for data on this website:
Shining Flatsedge — Cyperus bipartitus.  Montana Field Guide.  .  Retrieved on , from