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Western Sedge - Carex occidentalis
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.
Carex occidentalis is rare in the state, where it is at the northern edge of its range. It is known from 1 recent, verified collection from 2018 in Beaverhead County. Other reports and collections are unverified and may be misidentified, as the species is very similar to other sedge species. Data on population size and extent are lacking. Surveys are greatly needed to document the population size, extent and habitat of the verified location and to survey other areas of potentially suitable habitat. The identification of the historical collection by Shear in 1895 from Silver Bow County needs to be verified, as do any other potential collections or reports.
General Description
PLANTS: Western Sedge has short, creeping rhizomes (not conspicuous) and forms dense bunches with flowering stems that are sharply triangular and up to 80 cm tall. Source: (Ball in FNA 2002).
LEAVES: Blades are flat with slightly inrolled margins, 1.5 to 2.5(-3) mm wide. Sheaths are tight, green, and hyaline in the front. Ligules are less than 2mm long and as long wide. Sources: (Ball in FNA 2002; Hurd et al. 1998).
INFLORESCENCE: 4-10 spikes are tightly clustered towards the top, but more spaced towards the bottom. Each spike is oblong, 15-35 mm long by 6-10 mm. Spikes are androgynous with inconspicuous male flowers at the top. There are two stigmas. Sources: (Ball in FNA 2002; Hurd et al. 1998).
Phenology
Flowering and fruiting in June-July (Ball in FNA 2002).
Diagnostic Characteristics
Carex is a large genus, making individual species identification difficult at times. The bunch-forming growth form, elongate heads and elliptic perigynia are among the more diagnostic characteristics of this species among upland Carex. Mature fruit and a technical key are essential in order to separate this from closely related species.
Species Range
Montana Range
Range Descriptions
Native
Range Comments
Beaverhead and Madison Counties east to SD, south to CA and TX; most common in CO, UT AZ and NM (FNA 2002).
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
Recency
(Observations spanning multiple months or years are excluded from time charts)
Habitat
Western Sedge is occasionally to frequently found in dry grasslands and forests, generally at mid-elevations, but extending upward to sulalpine or alpine areas from 1,200 to 3,500 meters in elevation Sources: (Ball in FNA 2002; Hurd et al. 1998).
National Vegetation Classification System Groups Associated with this Species
Shrubland
Sagebrush Shrubland
Wetland and Riparian
Riparian Shrubland
Reproductive Characteristics
Spikes have inconspicuous male flowers at the top (androgynous).
Perigynia are green to straw-colored, but become brown at maturity and 2.5-4.5 mm long and 1.5-1.9 mm wide. They are smooth and shiny and are loosely ascending or spreading in the spikes. Their shape is oblong-elliptic and plano-convex. Their margins are sparingly serrulate above the middle, yet sharp, narrow, green, smooth, and shiny. The base of the body is somewhat spongy. Nerves are inconsipicuous or absent.
Beaks are abruptly narrowed from the body, serrulate, flat, shallowly to deeply bidentate, and 0.2-1.2 mm long.
Achene is oblong-orbicular, lenticular, light-brown at maturity, 1.3-2.4 mm long, and 0.9-1.5 mm wide.
Stigmas 2.
Stewardship Responsibility
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- Flora of North America Editorial Committee(FNA). 2002. Flora of North America north of Mexico. Vol. 23. Magnoliophyta: Commelinidae (in part): Cyperaceae. Oxford Univ. Press, New York. xxiv + 608 pp.
Hurd, E.G., N.L. Shaw, J. Mastrogiuseppe, L.C. Smithman, and S. Goodrich. 1998. Field Guide to Intermountain Sedges. General Technical Report RMS-GTR-10. Ogden, UT: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 282 pp.- 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.
- Web Search Engines for Articles on "Western Sedge"
