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.

Carex acutiformis
Carex acutiformis
(lesser pond sedge)

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Carex acutiformis Ehrh.

Common name: lesser pond sedge

Synonyms and Other Names: lesser pond sedge; European lake sedge

Taxonomy: available through www.itis.govITIS logo

Identification: Plants colonial; rhizomes long-creeping. Culms central, coarse, trigonous, 55–130 cm, scabrous-angled. Leaves: basal sheaths pale green to brownish or red tinged; ligules 5–14 mm; blades glaucous, M-shaped, (4.5–)5.5–12(–20) mm wide, glabrous. Inflorescences 15–35 cm; proximal 2–5 spikes pistillate, ascending; distal spikes erect; terminal 1–2(–3) spikes staminate. Pistillate scales lanceolate, acute to acuminate, glabrous, at least the proximal with scabrous awn to 3.5 mm. Perigynia ascending, ± glaucous, often strongly red dotted, ± strongly 12–18-veined, thin-walled, narrowly ovoid, flattened-trigonous, 3–4.5 × 1.4–2.1 mm, glabrous; beak 0.3–0.6 mm, emarginate to weakly bidentulate, teeth to 0.2 mm. 2n = 78.Superficially resembles C. aquatilis, but is larger, has 3 stigmas, and has strongly veined perigynia 3–4.5 mm.

Size: to 0.75 m tall.

Native Range: Eurasia and Africa

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 Carex acutiformis are found here.

StateFirst ObservedLast ObservedTotal HUCs with observations†HUCs with observations†
CT200820081New England Region
DE200820081Mid Atlantic Region
IN195120082Ohio Region; St. Joseph
MD200820081Mid Atlantic Region
MA186520081New England Region
MI199820142Boardman-Charlevoix; Lake Michigan
NY200820081Long Island
RI200820081New England Region

Table last updated 7/16/2024

† Populations may not be currently present.

Ecology: Carex acutiformis is a monocotyledonous perennial with laterally extending rhizomes and, in its native range, is capable of forming dense stands up to 1 m high (Hirose et al. 1989). It is found in open swamps, wet, open thickets, marsh edges, sedge meadows, eutrophic fens, and along the shores of ponds, rivers, and lakes, 0–300 m from shoreline. In dense stands of C. acutiformis, individual plants tend to have greater leaf area and higher leaf nitrogen concentrations in the top-most leaves, maximizing individual photosynthetic capacity (Hirose et al. 1989, Schieving et al. 1992). However, C. acutiformis also has a high leaf area ratio in general relative to other fen sedges (Konings et al. 1992). It also has a relatively high efficiency in nitrogen (N) use, but is less efficient in phosphorus (P) use (Aerts and de Caluwe 1994, Konings et al. 1992).

Tall Carex species, such as C. acutiformis, may dominate fens that are rainwater fed and base-poor relative to short Carex species, which tend to dominate base-rich fens (Verhoeven and Arts 1992). In acidic waters (e.g., base-poor fens), the decomposition of cellulose in C. acutiformus plant matter may occur slowly, preventing the full release of nutrients until 3-4 years after death and immobilizing N and P for a longer period of time relative to other sedges (Aerts and de Caluwe 1997, Verhoeven and Arts 1992). However, because C. acutiformis produces more leaf litter than most sedges, it may actually facilitate a higher rate of nutrient cycling than what the other sedges attain (Aerts and de Caluwe 1997).

Germination occurs at temperatures above 15°C, peak emergence is in early summer, and fruiting occurs June–August (Schütz 1998). Percent emergence (from seed) is very low at shaded sites, possibly due to a relatively high minimum temperature requirement. In European populations, the production of viable seed in C. acutiformis is low relative to that of other sedges, suggesting that clonal reproduction is favored (Schütz 1998).

Means of Introduction: It is suspected that this plant was introduced through hay from Europe. There are concerns that it may spread from roadside ditches where it occurs. The seeds, rhizome and root masses of the plant may attach to animals or possibly road maintenance equipment/ vehicles passing through a stand of this plant.  

Status: Established

Impact of Introduction: Carex acutiformis forms large, glaucous clones where it is established but is, as yet, not spreading aggressivly into adjacent habitats. Carex acutiformis dominated a 6 acre open marsh of native trees, shrubs, vines, grasses, forbs, and ferns after introduction. It formed a dense subcanopy of accumulated leaf litter in the introduced area (Catling and Kostiuk 2003).

Native Canadian butterflies were known to be restricted to native Carex lacustris as a larval host plant, but its absence in the area, coupled with dominance of its close relative, Carex acutiformis, provides strong circumstantial evidence of the use of the latter as larval food by Broad-winged Skippers, Browns including the Eyed Brown, Dion Skippers and Mulberry Wings. Because the introduced Carex acutiformis has a broad distribution, these butterflies have been able to increase their distribution by switching to habitats dominated by this invasive species (Catling and Kostiuk 2014).


References: (click for full references)

Aerts, R. and H. De Caluwe. 1997. Nutritional and plant-mediated controls on leaf litter decomposition of Carex species. Ecology 78(1):244—260.

Aerts, R., and H. de Caluwe. 1995. Interspecific and intraspecific difference in shoot and leaf lifespan of four Carex species which differ in maximum dry matter production. Oecologia 102(4): 467—477.

Aerts, R. and H. De Caluwe. 1994. Nitrogen use efficiency of Carex species in relation to nitrogen supply. Ecology 75(8):2362—2372.

Brouillet, L., F. Coursol, and M. Favreau. 2006. VASCAN, the Database of Vascular Plants of Canada. Herbier Marie-Victorin, Institut de recherche en biologie végétale, Université de Montréal.

Catling, P.M. 2005. New "top of the list" invasive plants of natural habitats in Canada. Botanical Electronic News 345: 1—5.  Available http://www.ou.edu/cas/botany-micro/ben/ben345.html. Accessed 2011.

Catling, P.M., and B. Kostiuk. 2003. Carex acutiformis dominance of a cryptic invasive sedge at Ottawa. Botanical Electronic News 315: 1—6.  Available http://www.ou.edu/cas/botany-micro/ben/ben315.html. Acessed 2011.

Catling, P.M., and B. Kostiuk. 2014. Use of a marsh dominated by the introduced European Lake Sedge, Carex acutiformis, by highly localized native butterflies. Canadian Field-Naturalist 128(4):358-362

Cayouette, J. and P.M. Catling. 1992. Hybridization in the Genus Carex with special reference to North America. Botanical Review 58(4): 351—438.

Crovello, T.J., C.A. Keller, and J.T. Kartesz. 1983. The vascular plants of Indiana: A computer based checklist. University of Notre Dame Press, Notre Dame.

Cullina, M.D., B. Connolly, B. Sorrie, and P. Somers. 2011. The vascular plants of Massachusetts: A county checklist, first revision. Massachusetts Natural Heritage & Endangered Species Program, Massachusetts Division of Fisheries and Wildlife, Westborough.

Curran, W.S., D.D. Lingenfelter, and L. Garling. 2009. Conservation Tillage Series: An introduction to weed management for conservation tillage systems. Pennsylvania State University, College of Agricultural Sciences: Agricultural Reserach and Cooperative Extension University Park, PA. 8 pp.

Darbyshire, S. J. & L. E. Pavlick. 1997. Nomenclatural Notes on North American Grasses. Phytologia 83: 73–78.

Dowhan, J.J. 1979. Preliminary checklist of the vascular flora of Connecticut (growing without cultivation). State Geological and Natural History Survey of Connecticut, Natural Resources Center, Department of Environmental Protection. Hartford.

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

Frye, C.T.,and C. Lea. 2001. Atlas and annotated list of Carex (Cyperaceae) of Maryland and the District of Columbia. The Maryland Naturalist 44(2): 41-108.

Glenn, S.D. (ed.). 2013. New York Metropolitan Flora database. New York Metropolitan Flora Project, Brooklyn Botanic Garden, New York.

Hermann, F. J. 1952. Carex acutiformis in Indiana. The American Midland Naturalist 48(1):36.

Hirose, T., M.J.A. Werger, and J.W.A. van Rheenen. 1989. Canopy development and leaf nitrogen distribution in a stand of Carex acutiformis. Ecology 70(6):1610—1618.

Konings, H., J.T.A. Verhoeven, and R. De Groot. 1992. Growth characteristics and seasonal allocation patterns of biomass and nutrients in Carex species growing in floating fens. Plant and Soil 147:183—196.

Konings, H., E. Koot, and T. Tijman-de Wolf. 1989. Growth characteristics, nutrient allocation and photosynthesis of Carex species from floating fens. Oecologia 80: 111—121.

Lawniczak, A.E., J. Zbierska, A. Choinski, and W. Szczepaniak. 2010. Response of emergent macrophytes to hydrological changes in a shallow lake, with special reference to nutrient cycling. Hydrobiologia 656: 243—254.

MICHIGAN FLORA ONLINE. A. A. Reznicek, E. G. Voss, & B. S. Walters. February 2011. University of Michigan. Web. October 29, 2019. https://michiganflora.net/species.aspx?id=894.

Mitchell, R.S. (ed.). 1986. A checklist of New York State plants. Contributions of a Flora of New York State, Checklist III. New York State Bulletin No. 458. New York State Museum, Albany.

New York Flora Association. 1990. Preliminary vouchered atlas of New York State flora, ed. 1. New York State Museum Institute, Albany.

Reznicek, A. - University of Michigan, Ann Arbor, MI.

Schieving, F., T.L. Pons, M.J.A. Werger, and T. Hirose. 1992. The vertical distribution of nitrogen and photosynthetic activity at different plant densities in Carex acutiformis. Plant and Soil 14:9—17.

Schütz, W. 1998. Seed dormancy cycles and germination phonologies in sedges (Carex) from various habitats. Wetlands 18(2):288—297.

U.S. Army Corps of Engineers (USACE). 2011a. Aquatic herbicides. 8 pp.

U.S. Army Corps of Engineers (USACE). 2011b. Manual harvest and mechanical control methods. 9 pp.

Verhoeven, J.T.A. and H.H.M. Arts. 1992. Carex litter decomposition and nutrient release in mires with different water chemistry. Aquatic Botany 43:365—377.

Vymazal, J. 2011. Plants used in constructed wetlands with horizontal subsurface flow: a review. Hydrobiologia 674: 133—156.

Vymazal, J., and L. Kröpfelová 2008. Wastewater treatment in constructed wetlands with horizontal sub-surface flow: environmental pollution. Volume 14. Springer Science. Ch. 6.

Weldy, Troy, David Werier, and Andrew Nelson. 2019 New York Flora Atlas. [S. M. Landry and K. N. Campbell (original application development), USF Water Institute. University of South Florida]. New York Flora Association, Albany, New York.

Other Resources:
USDA/NRCS Plants Database

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

Revision Date: 10/4/2023

Citation Information:
Cao, L., J. Larson, L. Berent, and A. Fusaro, 2024, Carex acutiformis Ehrh.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, https://nas.er.usgs.gov/queries/FactSheet.aspx?speciesID=2704, Revision Date: 10/4/2023, Access Date: 7/16/2024

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.


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Citation information: U.S. Geological Survey. [2024]. Nonindigenous Aquatic Species Database. Gainesville, Florida. Accessed [7/16/2024].

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