Rare Species Guide

  Basis for Listing

Carex grayi (Gray’s sedge) reaches the northwestern limit of its range in Minnesota, where it is found in mature alluvial forests, predominately along the Mississippi River from about Anoka (Anoka County), downstream to the Iowa border (Eastern Broadleaf Forest Province). There are also a few scattered records from along major tributaries such as the Zumbro and Cannon rivers as well as the Blue Earth River, the Rum River (Laurentian Mixed Forest Province), and a few others.  In all cases, C. grayi is quite rare and dependent on complex and dynamic riverine processes. Compounding the issues of rarity and limited habitat are the increasing demands for recreation, transportation, and industry that are being placed upon Minnesota rivers.  For these reasons, C. grayi was designated a species of special concern in 2013.

  Description

The stems of C. grayi are clumped and can reach 80 cm (30 in.) in length. The rhizomes can be about 3 cm (1 in.) long, but often they are not apparent. The leaf blades have a maximum width of about 1.0 cm (0.4 in.), and the sheaths of the basal leaves are dark red or maroon. The terminal spike has only male flowers and is 1-6 cm (0.4-2.4 in.) long. There are 1-2 spherical female spikes below the single male spike, each is 2.5-4.0 cm (1.0-1.6 in.) across, with 8-35 perigynia radiating in all directions from what appears to be a single point. The perigynia are rhombic-ovoid in shape, tapered to the base, 1.2-1.8 cm (0.5-0.7 in.) long, 4-7 mm (0.16-0.28 in.) wide, with 6-12 veins visible from a single view (without turning the perigynia), smooth or covered with short and stiff hairs. The beak of each perigynium is 2-4 mm (0.08-0.16 in.) long and barely distinct from the body. The achenes are ellipsoid to obovoid in shape (Ball and Reznicek 2002; Reznicek and Ball 1974.) In general aspect, C. grayi is a very conspicuous sedge, with uniquely large spherical spikes that look something like a medieval mace or a sea urchin. It could only be confused with C. intumescens (greater bladder sedge).  However, the spikes of C. intumescens are small, no more than 2.5 cm (1.0 in.) long, and usually have fewer than 10 perigynia, and the perigynia all point more or less upwards, rather than radiating in all directions.

  Habitat

Carex grayi occurs in alluvial forests of the type dominated by Populus deltoides (cottonwood) and Acer saccharinum (silver maple), with lesser amounts of Salix nigra (black willow), Fraxinus pennsylvanica (green ash), Ulmus americanus (American elm), Betula nigra (river birch), Quercus bicolor (swamp white oak), and Celtis occidentalis (hackberry). Under natural conditions, these forests would be flooded nearly every spring, becoming surface-dry by late summer. Soils include a variety of water-borne sediments, predominately silt but sometimes coarser material such as sand.

  Biology / Life History

Although there is very little published information about the biology of C. grayi, a great deal can be surmised from the type of habitat it depends upon. For example, C. grayi is clearly very tolerant of spring flooding as well as the scouring and sediment deposition that accompanies flooding along major rivers. Its fruits (perigynia) are unusually large and inflated, so it is easy to conclude that they float well and disperse downstream during any particular flood event. Carex grayi is also very tolerant of shade.

  Conservation / Management

Forests where C. grayi occurs must remain intact. Logging or other land clearing activities are clearly destructive to the habitat. Even logging that is done in such a way as to allow natural regeneration of the trees will cause the loss of existing C. grayi populations and deprive any founding populations of suitable habitat for a very long time. Keeping floodplain forests intact should not represent too great a hardship, since most floodplain tree species have very little commercial value. Regenerating any tree cover in an active floodplain is so difficult that most experienced land management agencies endeavor to keep existing forests intact.

In addition to protecting tree cover, it is critically important to preserve the natural hydrologic integrity of the river. Activities that would prevent floods from occurring on natural floodplains may seem like a reasonable thing to do and in some cases may be necessary in order to protect existing dwellings and infrastructure, but the natural communities that depend on flooding would suffer as a consequence.

  Best Time to Search

The best time to search for C. grayi is when mature perigynia (fruit) are present, which is normally between about June 15 and September 10. If river levels remain high in spring and early summer, than maturation dates will be later.

  Authors/Revisions

Welby R. Smith (MNDNR), 2018

(Note: all content ©MNDNR)

  References and Additional Information

Ball, P. W., and A. A. Reznicek. 2002. Carex. Pages 254-572 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.

Minnesota Department of Natural Resources. 2005. Field guide to the native plant communities of Minnesota: the eastern broadleaf forest province. Ecological Land Classification Program, Minnesota County Biological Survey, and Natural Heritage and Nongame Research Program. Minnesota Department of Natural Resources, St. Paul, Minnesota. 394 pp.

NatureServe. 2009. NatureServe Explorer: An online encyclopedia of life [web application]. Version 7.1. NatureServe, Arlington, Virginia.

Reznicek, A. A. 2002. Carex sect. Lupulinae. Pages 511-514 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.

Reznicek, A. A., and P.W. Ball. 1974. The taxonomy of Carex series Lupulinae in Canada. Canadian Journal of Botany. 52(11):2387-2399.

Smith, W. R. 2018. Sedges and rushes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 696 pp.