Carex acutiformis Ehrh.

Common Name: Lesser pond sedge

Synonyms and Other Names:

lesser pond sedge; European lake sedge

Fornax ( Info

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

Great Lakes Nonindigenous Occurrences: Lake Michigan Drainage - 1951introduced: Ontario; Connecticut, Indiana, Massachusetts, Maryland, Michigan, New York

Ottawa, Canda. (Catling 2005)

Table 1. Great Lakes region nonindigenous occurrences, the earliest and latest observations in each state/province, 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.

Full list of USGS occurrences

State/ProvinceYear of earliest observationYear of last observationTotal HUCs with observations†HUCs with observations†
Indiana195119821St. Joseph

Table last updated 9/30/2019

† 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

Great Lakes Impacts:  

Carex acutiformis has a moderate environmental impact in the Great Lakes.
Currently, there are few reported populations of C. acutiformis in the Great Lakes, suggesting that it is a relatively rare introduction. However, the swamp sedge is often misidentified as the native water sedge (C. aquatilis), which could limit its documentation. It does not appear to disperse well across long distances, but where it establishes, it is capable of spreading locally via rhizomes and displacing native species (A. Reznicek, pers. comm.). In 1982, C. acutiformis was observed forming a near monoculture around the entirety of St. Joseph Lake, South Bend, IN. Similarly, C. acutiformis was discovered dominating a 6-acre open marsh area in the Stony Swamp Conservation Area near Ottawa, ON. In this conservation area, C. acutiformis co-existed with native trees but had displaced nearly all other native plants in both open water and some relatively dry areas (Catling and Kostiuk 2003). Thus, this species may be a very serious threat to native vegetation on a local geographic scale due to its ability to spread rapidly via vegetative growth and out-compete native species for nutrients and light (Catling and Kostiuk 2003; A. Reznicek, pers. comm.) It may also smother native plants via accumulation of its excess litter (Catling and Kostiuk 2003).

Carex acutiformis has been found to have a longer lifespan and create more above ground plant biomass than three of the native sedge species: C. diandra, C. rostrata, and C. lasiocarpa (Aerts and Caluwe 1995, Konings et al. 1989).  Carex acutiformis was also the most efficient  in nitrogen use relative to production of biomass (Konings et al. 1992).

As of 1992, a total of 253 Carex hybrids have been reported in North America. This indicates that this genus is highly capable of hybridization, and invasive species, such as C. acutiformis, may be a genetic threat to native sedge species (Cayouette and Catling 1992).

There is little or no evidence to support that Carex acutiformis has significant socio-economic impacts in the Great Lakes.

There is little or no evidence to support that Carex acutiformis has significant beneficial effects in the Great Lakes.
Carex acutiformis has been used in horizontal subsurface-flow constructed wetlands in Denmark, Slovenia, and Germany (Vymazal 2011). Carex acutiformis (in combination with Spartina pectinata and Phragmites australis) was successful in removing 91.6% of the ammonium concentration and 80.6% of organic nitrogen in a treatment wetland in Germany, which was developed to treat dairy farm wastewater (Vymazal and Kröpfelová 2008).

Management: Regulations (pertaining to the Great Lakes region)
Based on its competitive dominance in Stony Swamp, Ottawa, Ontario, C. acutiformis was identified as a high priority invasive plant by the Canada Botanical Association in 2004, ranking 14th overall among invasive plants (Catling 2005).

Note: Check federal, state/provincial, and local regulations for the most up-to-date information.

There are no known biological control methods for this species.

Harvesting, either mechanically or by hand, may be a viable option, depending on site conditions. Extreme care should be taken to remove all parts of the roots system and rhizomes to prevent further spread of the species. This method is unlikely to eradicate swamp sedge, but it will help to prevent population expansion. Physical control methods are most effective when completed before seed production (USACE 2011b).
Seeds do not germinate when they are 7 cm below the soil surface (Schütz 1998). Thus, tilling the soil to push the existing seeds deeper into the substrate may be an effective method for reducing the prevalence of swamp sedge (Curran et al. 2009).

Carex acutiformis does not extend into open water deeper than 55 cm, and it able to cope with low water levels. Stands of C. acutiformis did not decrease immediately after moderate reduction in water level, suggesting that water level alteration may not be an effective form of control (Lawniczak et al. 2010).

Currently no peer-reviewed literature examines the efficacy of herbicides against swamp sedge. According to the Center for Ecology and Hydrology all sedges are susceptible to glyphosate; an application in mid to late summer will maximize translocation and control of rhizomes (USACE 2011a). Imazapyr has also been effective in controlling some sedge species (USACE 2011a).

Note: Check state/provincial and local regulations for the most up-to-date information regarding permits for control methods. Follow all label instructions.

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.

Catling, P.M. 2005. New "top of the list" invasive plants of natural habitats in Canada. Botanical Electronic News 345: 1—5.  Available 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 Acessed 2011.

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

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.

Flora of North America.  2008.

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.

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.


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

Contributing Agencies:

Revision Date: 6/15/2012

Citation for this information:
Cao, L., J. Larson, L. Berent, and A. Fusaro, 2020, Carex acutiformis Ehrh.: U.S. Geological Survey, Nonindigenous Aquatic Species Database, Gainesville, FL, and NOAA Great Lakes Aquatic Nonindigenous Species Information System, Ann Arbor, MI,, Revision Date: 6/15/2012, Access Date: 2/27/2020

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.