The Nonindigenous Occurrences section of the NAS species profiles has a new structure. The section is now dynamically updated from the NAS database to ensure that it contains the most current and accurate information. Occurrences are summarized in Table 1, alphabetically by state, with years of earliest and most recent observations, and the tally and names of drainages where the species was observed. The table contains hyperlinks to collections tables of specimens based on the states, years, and drainages selected. References to specimens that were not obtained through sighting reports and personal communications are found through the hyperlink in the Table 1 caption or through the individual specimens linked in the collections tables.

Juncus compressus
Juncus compressus
(roundfruit rush)
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Juncus compressus Jacq.

Common name: roundfruit rush

Synonyms and Other Names: Compressed rush, roundfruit rush, Juncus bulbosus Linnaeus, 1762, J. supinus Moench

Taxonomy: available through www.itis.govITIS logo

Identification: Juncus compressus is a perennial graminoid (grass-like) herb, about 80 cm in height. Rhizomes are short-creeping or densely branching.  When densely branching, the plant appears cespitose (grows in tufts).  There are 1-3 cataphylls, and 1-2 leaves, which are basal and cauline (belonging to the stem), with scarious to membranous auricles 0.3-0.5 mm in length.  The leaf blade is flat to slightly channeled, measuring 5-35 cm long and 0.8-2 mm wide, with margins entire (without toothing or division).  Inflorescences consist of 5-60 flowers, measure 1.5-8 cm, and are lax, and loose to moderately congested.  The primary bract usually exceeds the inflorescence.  Individual flowers have two bracteoles, and tepals that are brownish, ovate to oblong, and measure 1.7-2.7 mm.   Inner and outer tepal series are nearly equal, with the apex obtuse.  Flowers have six stamens, with filaments measuring 0.5-0.7 mm and anthers 0.6-1 mm.  The style measures about 0.3 mm.  Seed capsules are brown or darker, pseudo-3-locular, widely ellipsoid to obovoid, and measure 2.5-3.5 x 1.4-1.8 mm, exceeding the tepals.  Individual seeds are light brown, ellipsoid to lunate, measuring 0.35-0.556 mm, and are not tailed. Chromosome number is 2n = 44.

Juncus compressus is easy to confuse with J. gerardii, another non-native species in the Great Lakes (Online Atlas of British & Irish Flora 2012).

Size: 10-80 cm (Evergreen 2012)

Native Range: Eurasia

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Nonindigenous Occurrences:

Table 1. States with nonindigenous occurrences, the earliest and latest observations in each state, and the tally and names of HUCs with observations†. Names and dates are hyperlinked to their relevant specimen records. The list of references for all nonindigenous occurrences of Juncus compressus are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
IL198220084Chicago; Des Plaines; Little Calumet-Galien; Upper Fox
IN198720084Chicago; Kankakee; Little Calumet-Galien; Ohio Region
ME200820081New England Region
MD200820081Mid Atlantic Region
MI1980200813Detroit; Flint; Great Lakes Region; Huron; Kawkawlin-Pine; Lake Huron; Lake St. Clair; Little Calumet-Galien; Pigeon-Wiscoggin; Raisin; Saginaw; Shiawassee; Tittabawassee
MN196220082Roseau; Two Rivers
NE200820081Missouri Region
NY189518952Lake Ontario; Seneca
WI1974200910Bad-Montreal; Fox; Lower Fox; Manitowoc-Sheboygan; Northwestern Lake Michigan; Pike-Root; Rock; Southwestern Lake Superior; Upper Fox; Upper Rock

Table last updated 1/24/2021

† Populations may not be currently present.

* HUCs are not listed for states where the observation(s) cannot be approximated to a HUC (e.g. state centroids or Canadian provinces).

Ecology: Juncus compressus favors calcareous wetlands and is often associated with disturbed habitats, such as ditches, roadsides, railroads, and canal banks. Its ideal substrate is moist loamy/clay soil; J. compressus can also grow in water at a depth of up to 1 meter (Centre for Aquatic Plant Management 2004). It is frequently found in saline or alkaline soils and typically grows at elevations of 1500—2100 m (Brickell 2003). This species excels with partial to full sun and warm temperatures (Brickell 2003). Flowering and fruiting occurs in late spring or early summer, with the peak period for seed release occurring in fall (Skoglund 1989 in Benvenuti 2007). It can also spread vegetative through rhizome growth; fragments can lead to the development of an entire new plant.

Means of Introduction: Juncus compressus was brought to North America by the American military as feed for their horses (Evergreen Plant Database 2008).

Status: Established

Impact of Introduction: Competes for space.

References: (click for full references)

Benvenuti, S. 2007. Weed seed movement and dispersal strategies in the agricultural environment. Weed Biology and Management 7:141—157. Available http://onlinelibrary.wiley.com/doi/10.1111/j.1445-6664.2007.00249.x/pdf

Brickell, C. (ed.) 2003. RHS A-Z Encyclopedia of Garden Plants. Third edition. Dorling Kindersley, London.

Centre for Aquatic Plant Management. 2004. Information Sheet 2: Reeds, Rushes, Grasses and Sedges. Centre for Ecology & Hydrology, Natural Environment Research Council. Wallingford, Oxfordshire, United Kingdom. 2 pp.

Cosyns, E., S. Claerbout, I. Lamoot, and M. Hoffmann. 2005. Endozoochorous seed dispersal by cattle and horse in a spatially heterogeneous landscape. Plant Ecology 178(2):149—162.

Evergreen Native Plant Database. 2012. Juncus compressus. Available http://nativeplants.evergreen.ca/search/view-plant.php?ID=01291. Accessed 23 July 2012.

Flora of North America.  2008.  www.eFloras.org

Martin, A.C., H.S. Zim, and A.L. Nelson. 1951. American wildlife and plant: A guide to wildlife food habits. Dover Publications, Inc., New York, New York. 500 pp.

Michalski, S.G., and W. Durka. 2007. Synchronous pulsed flowering: analysis of the flowering phenology in Juncus (Juncaceae). Annals of Botany 100:1271—1285.

Online Atlas of British & Irish Flora. 2012. Juncus compressus (Round-fruited Rush). Available http://www.brc.ac.uk/plantatlas/index.php?q=plant/juncus-compressus. Accessed 23 July 2012.

Sérandour, J., J. Wilson, W. Thuiller, P. Ravanel, G. Lempérière, and M. Raveton. 2010. Environmental drivers for Coquillettidia mosquito habitat selection: a method to highlight key field factors. Hydrobiologia 652:377—388.

Skoglund S.J. 1989. Seed dispersal agents in two regularly flooded river sites. Canadian Journal of Botany 68:754—760.

Stevens, M., and S. Hoag. 2003. Baltic Rush Juncus balticus Willd. Plant Guide. United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS). 5 pp.

Stuckey, R.S. 1981. Distributional history of Juncus compressus (Juncaceae) in North America. Canadian Field-Naturalist 95:167—171.

United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS). 2012a. The PLANTS Database. Available http://plants.usda.gov/java/. Accessed 23 July 2012.

United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS). 2012b. The PLANTS Database. Culturally Significant Plants. Available http://plants.usda.gov/java/factSheet?cultural=yes  Accessed 23 July 2012.

United States Department of Agriculture (USDA) Natural Resources Conservation Service (NRCS), PLANTS Team. 2012c. The PLANTS Database. Threatened & Endangered. Available http://plants.usda.gov/threat.html. Accessed 23 July 2012.

U.S. Environmental Protection Agency (USEPA). 2008. Predicting future introductions of nonindigenous species to the Great Lakes. Washington, DC.

Vincent, M.A., and A.W. Cusick. 1998. New records of alien species in the Ohio vascular flora. Ohio Journal of Science 98(2):10—17. Available https://kb.osu.edu/dspace/bitstream/handle/1811/23775/V098N2_010.pdf?sequence=1

Author: Cao, L., L. Berent, and A. Fusaro

Revision Date: 9/23/2012

Citation Information:
Cao, L., L. Berent, and A. Fusaro, 2021, Juncus compressus Jacq.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=2691, Revision Date: 9/23/2012, Access Date: 1/24/2021

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.


The data represented on this site vary in accuracy, scale, completeness, extent of coverage and origin. It is the user's responsibility to use these data consistent with their intended purpose and within stated limitations. We highly recommend reviewing metadata files prior to interpreting these data.

Citation information: U.S. Geological Survey. [2021]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [1/24/2021].

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