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Montana Field Guide

Montana Field Guides

Tapered Rush - Juncus acuminatus

Species of Concern

Global Rank: G5
State Rank: S1
* (see State Rank Reason below)

Agency Status
USFWS:
USFS:
BLM:
MNPS Threat Rank: 2
C-value: 5

External Links






State Rank Reason (see State Rank above)
Rare in Montana. Only known in the state from one wetland site in Teton County.
 
General Description
Short-rhizomatous, caespitose. Stems erect, terete, 40–80 cm, tufted. Leaves basal and cauline; blades subterete, 1–2 mm wide; auricles rounded. Inflorescence open with erect branches and clusters of 10 to 20+ flowers ca. 1 cm across; main bract shorter than the inflorescence. Flowers: prophylls absent; tepals green to light brown, 2–4 mm long, acuminate; stamens 3. Capsules 2–4 mm long, slightly exserted, tapering to the beak; seeds apiculate (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Phenology
Mature fruit in late July.

Diagnostic Characteristics
The septate leaves and flowers subtended by a single bract and having only 3 stamens separate J. acuminatus from our other non-rhizomatous rushes. Juncus is a large and difficult genus to distinguish, so a technical key should be consulted. Mature fruit is necessary for positive determination.

Species Range
Present
 


Range Comments
BC to NS south to most of U.S., Mexico, S. America, rare on the Great Plains. One collection from Teton County (Lesica 2012. Manual of Montana Vascular Plants. BRIT Press. Fort Worth, TX).

Summary of Observations Submitted for Montana
Number of Observations: 1

(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
Wet soil on the margins of ponds and marshes in the valley zone and on the plains.

Ecological Systems Associated with this Species
  • Commonly Associated with these Ecological Systems
    Wetland and Riparian Systems

References
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Citation for data on this website:
Tapered Rush — Juncus acuminatus.  Montana Field Guide.  .  Retrieved on , from