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Montana Field Guide

Montana Field Guides

Red-root Flatsedge - Cyperus erythrorhizos

Species of Concern
Native Species

Global Rank: G5
State Rank: S2?
(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)
Known in Montana from one Prairie County collection in 2008. Previous reports were based upon mis-identified specimens. Survey work in appropriate habitat would likely discover additional locations in Montana. Additional site and population information is needed to more precisely rank the species.
  • Details on Status Ranking and Review
    Red-root Flatsedge (Cyperus erythrorhizos) Conservation Status Review
    Review Date = 04/24/2013
    View State Conservation Rank Criteria
    Population Size

    Score2-3 - Very Small to Small: Population size is imprecisely known but is believed to be <10,000 individuals.

    CommentUndocumented though would appear to be small.

    Range Extent

    Score2-3 - Local or Regional Endemic: Species has a small to very small range, though its distribution is either imprecisely documented or information to precisely categorize it was lacking at the time its status was reviewed.

    Area of Occupancy

    Score3 - Very Low: Generally occurring in 3 or fewer Subwatersheds (6th Code HUC’s).

    Environmental Specificity

    Score1 - Moderate: Species is restricted to a specific habitat that is more widely distributed or to several restricted habitats and is typically dependent upon relatively unaltered, good-quality habitat (C Values of 5-7).


    ScoreNA - Rank factor not assessed.



    ScoreNA - Rank factor not assessed.


    Intrinsic Vulnerability

    Score0-1 - Low to Moderate Vulnerability.

    Raw Conservation Status Score

    Score 8 to 11 total points scored out of a possible 13 (Rarity factors only).

General Description
Caespitose annual. Stems ascending to erect, 10–70 cm. Leaves mainly basal, 2–9 mm wide, V- or W-shaped in cross-section. Inflorescence of hemispheric clusters of ovoid spikes of sessile spikelets. Spikelets cylindric, 3–10 mm long. Scales gold, apiculate, 1.5–2 mm long with 3 obscure, median veins. Flowers: stamens 3; style 3-branched. Achene elliptic, brown, 3-sided, 0.5–1 mm long, apiculate (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Fruit mature in August.

Diagnostic Characteristics
Similar species include C. rivularis, C. acuminatus and C. aristatus, but all have globose rather than elongate spikes.

Species Range
Montana Range Range Descriptions


Range Comments
Throughout most of temperate U.S., Mexico. Known from Prairie 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: 3

(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)

Reported elsewhere from valleys and lowlands, especially along the shores of major rivers.
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.
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Citation for data on this website:
Red-root Flatsedge — Cyperus erythrorhizos.  Montana Field Guide.  .  Retrieved on , from