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Montana Field Guide

Montana Field Guides

Schweinitz's Flatsedge - Cyperus schweinitzii
Other Names:  Schweinitz Flatsedge

Species of Concern
Native Species

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

Agency Status
MNPS Threat Rank: 4
C-value: 8

External Links

State Rank Reason (see State Rank above)
Rare in Montana, where it is currently known from a few widely scattered sandy sites.
General Description
Rhizomatous perennial. Stems erect, 10–40 cm, bulbous-based. Leaves basal and lower-cauline, 1–2 mm wide, U-shaped in cross-section. Inflorescence of ovoid spikes of sessile spikelets. Spikelets somewhat compressed, 6–12 mm long. Scales green to tan, apiculate, 2.5–3.5 mm long, prominently veined. Flowers: stamens 3; style 3-branched. Achene elliptic, brown, 3-sided, 2–2.5 mm long, apiculate (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Fruit mature in late June-July.

Diagnostic Characteristics
This is our only perennial Cyperus spp. and also the only one occurring in sandy, upland habitats.

Species Range
Montana Range


Range Comments
AB to QC south to WA, NM, TX, KY, NY and Mexico (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Observations in Montana Natural Heritage Program Database
Number of Observations: 51

(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)

Sparsely-vegetated, sandy-soiled, prairie grasslands on ridges and slopes often near sandstone outcrops or on sandy "blowouts". Commonly associated species include Oryzopsis hymenoides, Stipa comata, Sporobolus cryptandrus, Calamovilfa longifolia, Carex filifolia, Andropogon scoparius, Tradescantia occidentalis, Pinus ponderosa and Yucca glauca.
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

  • Additional ReferencesLegend:   View Online Publication
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    • Heidel, B.L., S.V. Cooper and C. Jean. 2000. Plant species of special concern and plant associations of Sheridan County, Montana. Report to U.S. Fish and Wildlife Service. Montana Natural Heritage Program, Helena, Montana. 96 p.
    • Lesica, P., M.T. Lavin, and P.F. Stickney. 2012. Manual of Montana Vascular Plants. Fort Worth, TX: BRIT Press. viii + 771 p.
    • USDA, Agricultural Research Service. 1980. [Letter of December 3 to L. Dean Culwell containing the herbarium list for plant specimens on file at the Livestock and Range Research Station]. 13 pp.
    • Vanderhorst, J.P., S.V. Cooper, and B.L. Heidel. 1998. Botanical and vegetation survey of Carter County, Montana. Unpublished report prepared for the Bureau of Land Management. Montana Natural Heritage Program, Helena. 116 pp. + app.
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Citation for data on this website:
Schweinitz's Flatsedge — Cyperus schweinitzii.  Montana Field Guide.  .  Retrieved on , from