Juncus patans - grooved rush

Family: Juncaceae
Wetland Indictor Status: FACW
The grooved rush has a lateral inflorescence.

 The grooved rush can be 30-90 cm tall.

 The grooved rush is strongly tuft.


General Species Description

The grooved rush is a perennial, native, emergent plant growing to a height of 30-90 cm. This species has creeping rhizomes and grows in strong tufts. Grooved rush has lateral inflorescence (involucral bract appears to be a continuation of the stem). The involucral bract is generally one third as long as the stem and end in a sharp point.  The stem is blue-green and round, bearing brownish, loose, pointed sheaths.


The leaves of the Juncus patans are reduced and bristle-like, if they are present at all.


Grooved rush appears to have lateral inflorescences because the involucral bract, which is round and erect, appears to be a continuation of the stem. The inflorescence is 2.5-9 cm in length and are open with more than 20 flowers. Individual flowers have  tepals (2-3.5 mm) which are greenish or brown, needle-like, stiff, with transparent margins spreading away from the the capsule. The capsule is almost as long as the tepals and appears enlarged and round.  This species usually has 6 stamens. Blooms June through August. 


The seeds are an oval shape and have a distinctive ridge along the entire length.. 


Juncus patans can be found primarily in saturated soils on the westside of the Cascades in Oregon.


You can find this member of the Juncaceae family in the Willamette Valley and Cascade Mountains, and south from there to Santa Barbara County in California.

Similar Species

Soft Rush (Juncus effusus) is similar and also has round stems with an apparent lateral inflorescence and is strongly tufted as well.  However this plant tends to be more robust with stout, sharp stems, and flowers that have only three stamen. Baltic rush (Juncus balticus) can be distinguished by its more delicate form and flowers with 6 stamens and tepals that are 3.5-5 mm long. The baltic rush is also primarily found in coastal areas.

Ecological Value

Grooved rush can be used by muskrats and nutria as a food source and as shelter by various wading birds. The strong tufts make it a good for erosion control.

Human Value

Erosion control and ecological balance.


Cooke, S. S., ed. 1997. A Field Guide to the Common Wetland Plants of Western Washington & Northwest Oregon. Seattle Audubon Society and Washington Native Plant Society. Seattle Audubon Society, Seattle WA, 254pp.


This page was created by:  Mike Houston

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