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 gerardii
Juncus gerardii
(saltmeadow rush)
Native Transplant

Copyright Info
Juncus gerardii Loisel.

Common name: saltmeadow rush

Synonyms and Other Names:

Black grass, blackgrass, Gerard’s rush, mud rush, saltmarsh rush, saltmeadow rush, Juncus gerardi Loisel., Juncus gerardii var. gerardii Loisel., Juncus gerardii var. pedicellatus Fernald

Taxonomy: available through www.itis.govITIS logo

Identification: Juncus gerardii is a perennial, loosely-tufted graminoid (grass-like) herb ranging from short to elongate, with extensive long-creeping rhizomes.  Stems are erect, measuring 25-75 cm long. Cataphylls (that provide the plant with protection and/or structural support) number 1-3.  Leaves number 1-4 and are basal (located on the lower parts of the stem) extending at least halfway up.  Auricles (ear-like protrusion at the base of leaves) measure 0.4-0.8 mm and are scarious (membranous, dry, brownish in color).  Leaf blades are flat or somewhat channeled, measuring 10-40 cm long by 1.5-3 mm wide, lacking cross-walls, with margins entire. 

Flowers: Inflorescence terminal, 3-15 cm long, loosely branched, the branches ascending, the flowers each with 2 involucral bractlets; perianth (the sterile portions of flower) segments dark brown with greenish midribs, 3-4.5 mm long, rounded, blunt, with incurved, hooded tips, the inner about the same length as the outer; stamens 6; anthers 1.3-1.6 mm long, about 3 times the length of the filaments. Inflorescences 10--30(--80)-flowered, usually loose and somewhat lax, 2--16 cm; primary bract rarely surpassing inflorescence. Flowers: bracteoles 2; tepals dark brown or blackish, lanceolate-ovate to oblong, 2.6--3.2(--3.8) mm; inner and outer series nearly equal, apex obtuse; stamens 6, filaments 0.4--0.7 mm, anthers 1.1--1.6(--1.8) mm; style 0.4 mm.

Fruits: Capsules, chestnut brown or brown egg-shaped (widely ellipsoid), equal to or just slightly surpassing the perianth segments; seeds dark brown, ellipsoid to lunate (pear-shaped), about 0.5-0.6 mm long, lacking tail-like appendages.   2n = ca. 80, 84.

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


Size: 25-75cm

Native Range: North American Atlantic

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 gerardii are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
CT200820081New England Region
IL186220133Chicago; Lake Michigan; Upper Illinois
IN200820082Wabash; Wildcat
ME200820081New England Region
MD200820081Mid Atlantic Region
MA200820081New England Region
MI186220085Huron; Lone Lake-Ocqueoc; Manistee; St. Clair; St. Clair-Detroit
MN200820083Minnesota; Two Rivers; Upper Red
NH200820081New England
NJ200820081Mid-Atlantic Region
NY1864200813Bronx; Hudson-Hoosic; Long Island; Lower Genesee; Lower Hudson; Lower Hudson; Middle Hudson; Oswego; Rondout; Sandy Hook-Staten Island; Seneca; Southern Long Island; Southwestern Lake Ontario
OH200820083Black-Rocky; Sandusky; Upper Ohio-Beaver
OR200820081Pacific Northwest Region
PA200820086Delaware; Lehigh; Lower Delaware; Lower Susquehanna-Penns; Upper Delaware; Upper Susquehanna-Lackawanna
RI200820081New England Region
WA200820081Pacific Northwest Region
WI200820083Manitowoc-Sheboygan; Pike-Root; Southwestern Lake Michigan

Table last updated 6/13/2024

† 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 gerardii forms extensive colonies in marshlands, exposed coastal estuary meadows, salt marshes just above high-tide line, and even in some inland environments such as natural pastures (Bouzillé et al. 1997). This species can typically be found in habitats that are exposed to regular grazing (Burnside et al. 2007). Juncus gerardii prefers non-saline, waterlogged soils, but is intolerant to flooding (Charpentier et al. 1998, Rozema et al. 1985). It can tolerate saline ecosystems, however increasing salinity levels decrease germination of seeds, seedling survival, and reduce vegetative growth of existing plants (Charpentier et al. 1998). This species is able to survive up to 15 years after the desalinization of a salt marsh (Röling et al. 2001 in Beyen and Meire 2003). Juncus gerardii can also grow in soils with elevated concentrations of iron and manganese combined, but is sensitive to high concentrations of either element individually (Rozema et al. 1985).

Seedling recruitment occurs in dry, uncovered areas where there is little competition for light (Bertness 1991 in Charpentier et al. 1998, Keddy and Ellis 1985 in Charpentier et al. 1998). Shoot emergence usually begins in March and ends in June, when water becomes a limiting factor (Bouzillé et al. 1997). Fertile shoots tend to grow taller than vegetative shoots (Bouzillé et al. 1997). Juncus gerardii typically flowers and produces fruit from May to August (Lady Bird Johnson Wildflower Center 2012).

Communities of J. gerardii expand by vegetative rhizomal growth, forming clonal populations (de Kroon and Schieving 1990 in Bouzillé et al. 1997). Growth and expansion of clonal populations of J. gerardii is not deterred by temporary cold spells, and initial research indicates that cold spells may be for stimulation of flowering (Bouzillé et al. 1997).

Means of Introduction: solid ballast

Status: Established

Impact of Introduction: Brackish invasive species

Remarks: Juncus gerardii is considered to be “naturalized” in the Great Lakes region. Even though it is not native to this ecosystem, it has integrated into natural plant communities.

References: (click for full references)

Bertness, M.D. 1991. Interspecific interactions among high marsh perennials in a New England salt marsh. Ecology 72: 125–137.

Beyen, W., and P. Meire. 2003. Ecohydrology of saline grasslands: Consequences for their restoration. Applied Vegetation Science 6: 153–160.

Bouzillé, J.B., A. Bonis, B. Clément, and M. Godeau. 1997. Growth patterns of Juncus gerardi clonal populations in a coastal habitat. Plant Ecology 132(1): 39–48.

Brewer, J.S., J.M. Levine, and M.D. Bertness. 1998. Interactive effects of elevation and burial with wrack on plant community structure in some Rhode Island salt marshes. Journal of Ecology 86: 125–136.

Burnside, N.G., C.B. Joyce, E. Puurmann, and D.M. Scott. 2007. Use of vegetation classification and plant indicators to assess grazing abandonment in Estonian coastal wetlands. Journal of Vegetation Science 18: 645–654.

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

Charpentier, A., F. Mesléard, and P. Grillas. 1998. The role of water level and salinity in the regulation of Juncus gerardi populations in former ricefields in southern France. Journal of Vegetation Science 9(3): 361–370.

College of the Environment and Life Sciences. 2012. Field Guide to the Shore of Rhode Island: Salt Marsh. The University of Rhode Island. Available http://www.uri.edu/cels/bio/rishores/saltmrsh.htm. Accessed 8 August 2012.

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.

de Kroon, H., and F. Schieving. 1990. Resource partitioning in relation to clonal growth strategy. In J. Van Groendahl and H. de Kroon, [eds.], Clonal growth in plants: regulation and function. SPB Academic Publishing, The Netherlands.

Ericson, L. 1981. Aspects of the shore vegetation of the Gulf of Bothnia. Wahlenbergia 7: 45–60. In Jutila, H. 1999. Effect of grazing on the vegetation of shore meadows along the Bothnian Sea, Finland. Plant Ecology 140: 77—88.

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

Invasive Plants Association of Wisconsin (IPAW). 2012. Herbicides for Weed Brush Control in Natural Areas. Available http://www.ipaw.org/herbicides.aspx. Accessed 23 July 2012.

Jutila, H. 1999. Effect of grazing on the vegetation of shore meadows along the Bothnian Sea, Finland. Plant Ecology 140: 77–88.

Jutila, H.M. 1998. Seed banks of grazed and ungrazed Baltic seashore meadows. Journal of Vegetation Science 9: 395–408.

Keddy, P.A., and T.H Ellis. 1985. Seedling recruitment of 11 wetland species along a water level gradient: shared or distinct responses. Canadian Journal of Botany 63: 1876–1879.

Klinkenberg, B. (Ed.). 2008. E-Flora BC: Electronic Atlas of the Plants of British Columbia. Lab for Advanced Spatial Analysis, Department of Geography, University of British Columbia, Vancouver. Available www.eflora.bc.ca.Database.

Lady Bird Johnson Wildflower Center. 2012. Juncus gerardii Loisel. Native Plant Database.The University of Texas at Austin. Available http://www.wildflower.org/plants/result.php?id_plant=JUGE. Accessed 8 August 2012.

Levine, J.M., J.S. Brewer, and M.D. Bertness. 1998. Nutrients, competition and plant zonation in the New England salt marsh. Journal of Ecology 86: 285–292.

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. in 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.

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.

Röling, Y., H. Slager, and H. Drost. 2001. Disappearance of halophyte vegetation caused by desalination in former estuaries. Landschap 18: 87–98. (In Dutch)

Rozema, J., E. Luppes, and R. Brockman. 1985. Differential response of salt-marsh species to variation of iron and manganese. Vegetatio 62: 293–301.

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.

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.

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 Teams. 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.

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

Revision Date: 1/16/2024

Citation Information:
Cao, L., L. Berent, and A. Fusaro, 2024, Juncus gerardii Loisel.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?SpeciesID=2673, Revision Date: 1/16/2024, Access Date: 6/13/2024

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. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [6/13/2024].

Contact us if you are using data from this site for a publication to make sure the data are being used appropriately and for potential co-authorship if warranted.

For general information and questions about the database, contact Wesley Daniel. For problems and technical issues, contact Matthew Neilson.