Carex laxiculmis var. copulata Schwein.
Basis for Listing
Carex laxiculmis is a characteristic plant of deciduous forests in eastern North America, but it is rather uncommon in the Midwest. This species is especially rare in Minnesota where it reaches the northwestern limit of its range in the Blufflands region in the southeastern corner of the state. Since the time of European settlement, habitat suitable for C. laxiculmis has been greatly reduced and very fragmented, and the loss of habitat from land conversion for agricultural and urban uses continues. Carex laxiculmis was originally listed as a special concern species in Minnesota in 1984, but because targeted survey efforts determined that it was much rarer than previously thought, it was reclassified as threatened in 1996.
Sedges are grass-like, perennial herbs that can be identified to the genus Carex by their three-ranked leaves, closed sheaths, and triangular (only occasionally round), mostly solid stems, with terminal inflorescence. Identifying a sedge to species is often difficult and positive identification usually requires mature perigynia (the structure that appears to be the seed or fruit but is actually a bract enclosing the ovary) to be present. The fruit enclosed by the perigynium is an achene (Gleason and Cronquist 1991). Carex laxiculmis has weak, slender, tufted stems with soft, lax, basal leaves that are roughened on the margins. The terminal spike is staminate, peduncled, equaling or usually much surpassing the upper pistillate spike. Pistillate spikes are widely separated, the lower on long spreading or curved peduncles up to 10 cm (4 in.) long. The upper peduncles are progressively shorter, but always much longer than their subtending sheaths. Although C. laxiculmis bears a close resemblance to the common C. blanda (charming sedge), it can be distinguished by the following combination of characters: plants are whitish-green to brownish at the base, pistillate spikes (especially the lower ones) have 1 or 2 staminate flowers at the base, perigynia are sharply triangular with a few stiff spreading hairs, and staminate scales cinnamon-tinged on the margins. The peduncles are long-spreading, a character that distinguishes it from C. blanda (Wheeler 1981, 1984; Gleason and Cronquist 1991).
Carex laxiculmis prefers lower portions of steep, north- to east-facing slopes in mesic deciduous forests dominated by Acer saccharum (sugar maple) and Tilia americana (basswood). However, several populations are recorded from stands of similar composition situated on the floor of small stream valleys and on the margins of groundwater seeps. Carex laxiculmis is usually found in clumps of several to a few dozen individual plants and may be locally abundant. It often occurs with other rare plants of rich forests.
Biology / Life History
Like many other sedges of rich hardwood forests, C. laxiculmis flowers in the spring. Fertile culms appear with the leaves in early to mid-spring. Perigynia are shed by early summer. Plants are visible throughout the summer months, but without perigynia are nearly indistinguishable from C. blanda.
Conservation / Management
Carex laxiculmis may have been overlooked in the past because it bears such a close resemblance to the common C. blanda. In addition, its suitable habitat has been greatly reduced and fragmented since the time of European settlement. Land conversion for agriculture as well as urban and rural housing are expected to continue, further reducing the habitat of this species. Timber harvest methods that cause soil compaction, erosion, the introduction of invasive non-native species, and increased light levels at ground level should be avoided in the vicinity of known populations of C. laxiculmis. Livestock grazing is also likely to be detrimental to this species.
Conservation Efforts in Minnesota
The Minnesota DNR County Biological Survey has been completed in southeast Minnesota. Several populations of C. laxiculmis occur on State Forests, state Wildlife Management Areas, and State Parks. These public lands are probably well protected from land conversion and cattle grazing, but management plans should also incorporate adequate protection for C. laxiculmis and its habitat.
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.
Gleason, H. A., and A. Cronquist. 1991. Manual of vascular plants of northeastern United States and adjacent Canada. Second Edition. New York Botanical Garden, Bronx, New York. 910 pp.
Minnesota County Biological Survey. 1994. Natural communities and rare species of Houston County. Minnesota County Biological Survey Biological Report No. 50. Minnesota Department of Natural Resources, St. Paul.
Minnesota County Biological Survey. 1994. Natural communities and rare species of Winona County. Minnesota County Biological Survey Biological Report No. 49. Minnesota Department of Natural Resources. St. Paul.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis. 320 pp.
Smith, W. R. 2018. Sedges and rushes of Minnesota: the complete guide to species identification. University of Minnesota Press, Minneapolis. 696 pp.
Wheeler, G. A. 1981. A study of the genus Carex in Minnesota. Dissertation, University of Minnesota, St. Paul. 501 pp.
Wheeler, G. A., and G. B. Ownbey. 1984. Annotated List of Minnesota Carices, with phytogeographical and ecological notes. Rhodora 86(846): 151-231.