Ambiguous Sedge

Carex amphibola Steud.

Carex amphibola var. amphibola
Troy Weldy

Monocotyledoneae (Monocots)
Cyperaceae (Sedge Family)
State Protection
Not Listed
Not listed or protected by New York State.
Federal Protection
Not Listed
State Conservation Status Rank
Apparently Secure in New York - Uncommon in New York but not rare; usually widespread, but may be rare in some parts of the state; possibly some cause for long-term concern due to declines or other factors.
Global Conservation Status Rank
Secure globally - Common in the world; widespread and abundant (but may be rare in some parts of its range).


Did you know?

The scientific name amphibola means ambiguous (Fernald 1970). This plant was briefly listed as historical within New York State, but it was rediscovered at two sites in Dutchess County (Astor Point and Vassar College).

State Ranking Justification

There are at least 20 known populations of this sedge and probably more exist. There are approximately ten historical populations. The current range is limited to the Hudson Valley and New York City. There has been confusion with the identification due to taxonomic changes and some people not keying specimens to variety (e.g. Carex grisea used to be called Carex amphibolia var. turgida, but many specimens are not keyed to variety). These plants tend to be in low-lying wet areas that are subject to periodic inundation. There may be some threat from invasive species and habitat alteration.

Short-term Trends

Overall, the number of sites where this species has been found has been relatively stable.

Long-term Trends

Carex amphibola is known from at least 10 sites in New York where plants have not been seen in many years. In some cases, they were last seen over 100 years ago. Most of these sites do not have precise locale information so relocating these populations could be difficult. Also, this taxon has been poorly understood over the past 100 years and this may have resulted in it being under-collected or under-observed. Therefore, long-term trends in New York are not clear.

Conservation and Management


One extant site is near an area where recreational activities take place but it is unclear if these activities are impacting the population of Carex amphibola. Other potential threats are unclear.

Research Needs

Surveys of these populations would help get a better understanding of how this sedge is doing in New York. There have also been past errors in the circumscription of this species (Naczi 1999), therefore all specimens of this species should be verified. In addition, specimens of Carex grisea and Carex styloflexa should be re-examined to determine if any of them are in fact Carex amphibola.



In New York, Carex amphibola occurs on slopes in mesic forests with a full canopy and at the base of upland slopes near the edge of freshwater tidal marshes and tidal mudflats (New York Natural Heritage Program 2005). A wide ranging habitat generalist, it occurs in mesic deciduous forests; usually in acidic loams on flood plains, slopes above streams, and uplands (Naczi and Bryson 2002). Dry to moist woods, meadows, and swales (Rhoads and Block 2000). Woods and fields (Gleason and Cronquist 1991). Calcareous hardwoods, rich slopes, rich woods, bottomlands and meadows (Fernald 1970).

Associated Ecological Communities

  • Appalachian oak-hickory forest (guide)
    A hardwood forest that occurs on well-drained sites, usually on ridgetops, upper slopes, or south- and west-facing slopes. The soils are usually loams or sandy loams. This is a broadly defined forest community with several regional and edaphic variants. The dominant trees include red oak, white oak, and/or black oak. Mixed with the oaks, usually at lower densities, are pignut, shagbark, and/or sweet pignut hickory.
  • Floodplain forest (guide)
    A hardwood forest that occurs on mineral soils on low terraces of river floodplains and river deltas. These sites are characterized by their flood regime; low areas are annually flooded in spring, and high areas are flooded irregularly.
  • Oak-tulip tree forest (guide)
    A hardwood forest that occurs on moist, well-drained sites in southeastern New York. The dominant trees include a mixture of five or more of the following: red oak, tulip tree, American beech, black birch, red maple, scarlet oak, black oak, and white oak.

Associated Species

  • Acer rubrum var. rubrum (common red maple)
  • Acer saccharum (sugar maple)
  • Betula lenta (black birch)
  • Carex cephalophora (oval-headed sedge)
  • Carex digitalis
  • Carex granularis (limestone-meadow sedge)
  • Carex laxiculmis
  • Carex laxiflora (loose-flowered sedge)
  • Carex pensylvanica (Pennsylvania sedge)
  • Carex sparganioides (bur-reed sedge)
  • Carya sp.
  • Hamamelis virginiana (witch-hazel)
  • Hemerocallis fulva (orange day-lily)
  • Quercus rubra (northern red oak)
  • Toxicodendron radicans ssp. radicans (eastern poison-ivy)
  • Vaccinium pallidum (hillside blueberry)
  • Viburnum acerifolium (maple-leaved viburnum)


New York State Distribution

In New York it is currently known in the Hudson River Valley from Putnam County north to Albany County. Historically, it is thought to have been widely scattered throughout much of New York south of the Adirondacks although many past occurrences may be based on misidentifications.

Global Distribution

Carex amphibola occurs from Massachusetts and Connecticut west to New York, Ontario, Michigan, Illinois, and Missouri south to Georgia, Oklahoma, and Texas. Since this species has long been poorly circumscribed it is best to only recognize the range of the species presented in recent literature.

Identification Comments

General Description

This sedge is a densely tufted grass-like plant with leaves 4.4-7 (occasionally as small as 3.7) mm wide. It has thin flowering/fruiting stalks (culms) that are 15-80 cm tall. Four to five (occasionally as few as three) elongated clusters of flowers/fruits (spikes) are distributed along the culm. The uppermost one is entirely staminate while the others are pistillate (Naczi and Bryson 2002).

Identifying Characteristics

Carex amphibola is short rhizomatous and densely cespitose. The bases of the culms are dark purple-red to a height of 0.3-2.4(-7.3) mm or very rarely they are brown at the base (magnification and good light should be used to determine color). The terminal staminate spike is 7-34 mm long on a peduncle 1.6-21(-37) mm long. The 2-3(-4) lateral pistillate spikes have 3-18 perigynia per spike. The perigynia are spirally arranged on the axis of the spike, obtusely triangular in cross-section, 1.5-1.9(-2.2) mm wide, and (2.2-)2.5-3.1 times as long as wide.

Best Life Stage for Proper Identification

The species can be confused with other closely related species when not in fruit. Therefore, the best time to identify this species is when it is in fruit. Ample specimens with mature fruits should be collected to verify the identification.

Similar Species

Carex grisea, which is much more common in New York, is superficially quite similar. The easiest way to distinguish the two in the field is that C. grisea has perigynia orbicular to suborbicular in cross-section as opposed to obtusely triangular and less turgid for C. amphibola. This can be somewhat subtle, is comparative in nature, and is best observed on mature perigynia. C. grisea also has very little or no tapering to the tiny beak. Also C. grisea generally grows in lower, sandier, more calcium rich sites than C. amphibola. Careful measurements of perigynia and achenes should be taken to distinguish these two species. Carex grisea has perigynia (1.8-)2-2.6 mm wide and 1.8-2.3(-2.6) times as long as wide and has achenes1.7-2.1(-2.2) mm wide. Carex amphibola has perigynia 1.5-1.9(-2.2) mm wide and (2.2-)2.5-3.1 times as long as wide and has achenes (1.3-)1.5-1.7(-1.8) mm wide. Carex hitchcockiana and Carex glaucodea have brown culm bases, not purple-red, and Carex hitchcockiana has hairy sheaths.

Best Time to See

Carex amphibola is in fruit from June to early July. The best time for surveys is during this period.

  • Fruiting

The time of year you would expect to find Ambiguous Sedge fruiting in New York.

Ambiguous Sedge Images


Ambiguous Sedge
Carex amphibola Steud.

  • Kingdom Plantae
    • Phylum Anthophyta
      • Class Monocotyledoneae (Monocots)
        • Order Cyperales
          • Family Cyperaceae (Sedge Family)

Additional Common Names

  • Eastern Narrowleaf Sedge
  • Sedge


  • Carex amphibola var. rigida (Bailey) Fern.

Comments on the Classification

Naczi (1999) unraveled a tangled history regarding C. amphibola and named a new species, C. planispicata, in the process. Carex planispicata (which is known as far north as central New Jersey and Pennsylvania) was first recognized by Bailey as C. grisea var. rigida. Bailey later placed this variety as a synonym under C. amphibola. Fernald later resurrected this taxon but called it C. amphibola var. rigida. Fernald's circumscription of C. amphibola var. amphibola and C. amphibola var. rigida do not align with C. amphibola Steud. and C. planispicata Naczi, respectively. Specimens Fernald cited for C. amphibola var. amphibola sensu Fernald are mostly C. planispicata with some C. bulbostylis and C. godfreyi (neither of which occur in New York), while specimens cited for C. amphibola var. rigida are mostly C. amphibola Steud., with some C. corrugata, C. godfreyi, and C. planispicata. As a result, Fernald's (1970) key is misleading. Only recent literature that uses new information from Naczi (1999) should be used to identify C. amphibola. Gleason and Cronquist's (1991) understanding of C. amphibola appears to be severely limited and includes in it, at least in part, C. grisea Wahl., C. corrugata Fern., C. planispicata Naczi, C. planispicata Naczi, and C. amphibola Steud. Their text should not be used to identify specimens of C. amphibola Steud. Carex amphibola is in section Griseae. Naczi and Bryson (2002) place section Oligocarpae as a synonym of section Griseae. The former Carex amphibola var. turgida is now called Carex grisea.

Additional Resources

Best Identification Reference

Naczi, R.F.C. and C.T. Bryson. 2002. Carex Linnaeus sect. Griseae (L.H. Bailey) Kükenthal. Pages 448-461 in Flora of North America Editorial Committee (editors), Flora of North America, north of Mexico, Volume 23, Magnoliophyta: Commelinidae (in part): Cyperaceae. Oxford University Press, New York, NY, USA. 608pp + xxiv.

Other References

Fernald, M.L. 1950. Gray's manual of botany. 8th edition. D. Van Nostrand, New York. 1632 pp.

Flora of North America Editorial Committee. 2002. Flora of North America, North of Mexico. Volume 23. Magnoliophyta: Commelinidae (in part): Cyperaceae. Oxford University Press, New York. 608 pp.

Gleason, Henry A. and A. Cronquist. 1991. Manual of Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York. 910 pp.

Holmgren, Noel. 1998. The Illustrated Companion to Gleason and Cronquist's Manual. Illustrations of the Vascular Plants of Northeastern United States and Adjacent Canada. The New York Botanical Garden, Bronx, New York.

Naczi, R.F.C. 1999. Carex planispicata, a widespread and frequent new species of Carex section Griseae (Cyperaceae) from the eastern United States of America. Journal of the Kentucky Academy of Sciences 60(1):37-44.

New York Natural Heritage Program. 2010. Biotics database. New York Natural Heritage Program. New York State Department of Environmental Conservation. Albany, NY.

New York Natural Heritage Program. 2024. New York Natural Heritage Program Databases. Albany, NY.

Reschke, Carol. 1990. Ecological communities of New York State. New York Natural Heritage Program, New York State Department of Environmental Conservation. Latham, NY. 96 pp. plus xi.

Rhoads, Ann F. and Timothy A. Block. 2000. The Plants of Pennsylvania, an Illustrated Manual. University of Pennsylvania Press, Philadelphia, PA.

Tucker, Gordon C. 1995. Preliminary keys to Carex (Cyperaceae) in New York State. New York Flora Association Newsletter 6(2):3-18. Available online at:

USDA, NRCS. 2004. The plants database, version 3.5 ( <>. National Plant Data Center <>, Baton Rouge, LA 70874-4490 USA.

Weldy, T. and D. Werier. 2010. New York flora atlas. [S.M. Landry, K.N. Campbell, and L.D. Mabe (original application development), Florida Center for Community Design and Research University of South Florida]. New York Flora Association, Albany, New York

Weldy, Troy W. 1998. Memorandum of conversation with Robert Naczi of April 28, 1998 on the taxonomy of Carex amphibola.


About This Guide

Information for this guide was last updated on: September 28, 2010

Please cite this page as:
New York Natural Heritage Program. 2024. Online Conservation Guide for Carex amphibola. Available from: Accessed February 26, 2024.