Rare Species Guide

  Basis for Listing

What we know about Carex muskingumensis (Muskingum sedge) in Minnesota is that it occurs primarily in floodplain forests along the Mississippi River, from the Iowa border north to about Little Falls (Morrison County) (Eastern Broadleaf Forest Province). There is an 1885 herbarium specimen of C. muskingumensis labeled “Center City”, Chisago County that was most likely collected along the St. Croix River, though there is no way to know for sure. The record from Steele County has been recently confirmed and is in a vernal pool, not directly associated with any river. Although our picture of this species is still incomplete, a general pattern is emerging.

It appears the vast majority of C. muskingumensis in Minnesota occur along a stretch of the Mississippi River that is managed for commercial barge traffic, sometimes to the detriment of native riverine habitats. The initial construction and operation of locks and dams on the Mississippi River in the 1930s was responsible for the destruction of large tracts of floodplain forest, which is circumstantial evidence of a decline in populations of C. muskingumensis. In many cases, the dams prevent the seasonal flooding that sustains floodplain forests, thereby degrading the surviving habitats of C. muskingumensis as well as other species that rely on periodic flooding to create optimal habitat conditions. For these reasons, C. muskingumensis was listed as special concern in 2013.

  Description

The stems of C. muskingumensis are clumped and can reach 100 cm (39 in.) in length. The rhizomes are stout and can be up to about 8 cm (3 in.) long. The leaves have a maximum width of about 5.0 mm (0.2 in.). The inflorescence is stiff, 4.0-9.0 cm (1.6-3.5 in.) long, and consists of about 6-12 spikes. Each spike has both male and female flowers, is linear-elliptic in shape, and tapered at both ends. They are 1.0-2.5 cm (0.4-2.0 in.) long, 3.5-6.0 mm (0.12-0.24 in.) wide, and loosely aggregated. The perigynia are lanceolate to narrowly elliptic in shape, deeply bidentate, closely appressed, 6.0-8.5 mm long (0.24-0.34 in.), 1.5-2.2 mm (0.06-0.09 in.) wide, and finely veined on both surfaces. The achenes are 2.0-2.7 mm (0.08-0.11 in.) long and 0.7-0.9 mm (0.03-0.04 in.) wide. The long narrow spikes and perigynia make positive identification fairly easy; nothing else in Minnesota looks similar.

It may be helpful to understand the peculiar vegetative culms of C. muskingumensis. The leaves are in the usual 3 columns, but the columns do not spiral as they rise up the stem; they line up, one directly above the other. The leaves on the fertile culms do this as well, but the fertile culms have fewer leaves that are more widely spaced, so the effect is not as pronounced.

  Habitat

Carex muskingumensis occurs primarily in floodplain forests along the Mississippi River. The forest canopy is typically composed of Populus deltoides (cottonwood) and Acer saccharinum (silver maple), and the soil is coarse or fine-grained sediments. Because of the frequent flood scouring and sediment deposition, relatively few species occur in these habitats, and those that do usually occur in low densities. As a result, the understory and ground layer in these forests is often almost barren, especially in the spring and early summer after a flood.

  Biology / Life History

Clearly C. muskingumensis is supremely adapted to withstand spring floods. It seems that any plant that manages to avoid being uprooted and washed downstream by rushing meltwater still faces the danger of being buried under sediment carried from upstream. This would seem to create nearly impossible circumstances for perennial plants to survive. Yet C. muskingumensis not only survives these conditions, it manages to thrive. How it manages this isn’t entirely clear, but it does have at least one very unusual adaptive strategy. The vegetative stems, which are typically annual structures, sometimes survive a second year, buried in sediments, and generate new stems from the nodes of the old stems. Furthermore, C. muskingumensis is notable for producing an abundance of vegetative stems.

  Conservation / Management

Floodplain forests are typically composed of only a few tree species, and most of them have little timber value. Still, logging operations are sometimes conducted in such habitats, sometimes with unintended consequences. Without a tree canopy, non-native invasive species such as Phalaris arundinacea (reed canary grass) and Lythrum salicaria (purple loosestrife) often gain a foot-hold and in time may dominate the habitat to the detriment of the native species. Water level manipulation is another apparent problem. It is controlled by the U.S. Army Corp of Engineers and is undertaken almost exclusively for the benefit of barge traffic. Floodplain forest habitats would benefit by a greater seasonal variation in water levels than current U.S. Army Corps of Engineers' procedures allow.

  Best Time to Search

A positive identification of C. muskingumensis requires mature perigynia, which can be expected from early July through to the end of September.

  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.

Mastrogiuseppe, J., P. E. Rothrock, A. C. Dibble, and A. A. Reznicek. 2002. Carex sect. Ovales. Pages 332-378 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.

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