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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)

Agency Status
MNPS Threat Rank:
C-value: 4

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 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

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

Observations in Montana Natural Heritage Program Database
Number of Observations: 6

(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.

Ecological Systems Associated with this Species

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Citation for data on this website:
Shining Flatsedge — Cyperus bipartitus.  Montana Field Guide.  .  Retrieved on , from