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Montana Field Guide

Montana Field Guides

Western Quillwort - Isoetes occidentalis
Other Names:  Isoetes lacustris var. paupercula

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Species of Concern
Native Species

Global Rank: G4G5
State Rank: S1
(see State Rank Reason below)
State Threat Score: No Known Threats
C-value: 9


Agency Status
USFWS:
USFS:
BLM:


 





State Rank Reason (see State Rank above)
DRAFT: Requesting feedback on the 2026 revised rank, factors, and State Rank Reason outlined below and in the Conservation Status Rank Report.
Isoetes occidentalis is extremely rare in Montana, being known from only two waterbodies. Population levels and potential trends are unknown. It is unknown if any significant threats currently exist to either of the populations. The one occurrence has not been surveyed since 1998, and the other occurrence was observed in both 2019 and 1976 but lacks detailed data. Surveys of the known populations are needed to document their current status, including population size and extent, habitat quality and potential threats.
Western Quillwort (Isoetes occidentalis) Conservation Status Summary
State Rank: S1
Review Date = 03/11/2026
See the complete Conservation Status Rank Report
How we calculate Conservation Status Ranks
 
General Description
Plants aquatic. Leaves to 20 cm, gradually tapering. Sporangia 3–6 mm long. Megaspores 0.4–0.8 mm wide (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Species Range
Montana Range Range Descriptions

Native
 


Range Comments
Alaska, British Columbia, and California, east to Montana, Wyoming and Colorado.

Observations in Montana Natural Heritage Program Database
Number of Observations: 4

(Click on the following maps and charts to see full sized version) Map Help and Descriptions
Relative Density

Recency

 

(Observations spanning multiple months or years are excluded from time charts)



Habitat
Our one record is from shallow water of a montane lake in Missoula County (Lesica et al. 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see here

National Vegetation Classification System Groups Associated with this Species
Open Water
Open Water
Open Water Classified in 2025 Land Cover


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

References
  • 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.
    • MTNHP Threat Assessment. 2021. State Threat Score Assignment and Assessment of Reported Threats from 2006 to 2021 for State-listed Vascular Plants. Botany Program, Montana Natural Heritage Program, Helena, Montana.
  • 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 "Western Quillwort"
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Citation for data on this website:
Western Quillwort — Isoetes occidentalis.  Montana Field Guide.  .  Retrieved on , from