Carex obtusata Lilj.
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Basis for Listing
In Minnesota, Carex obtusata is an uncommon inhabitant of sandy prairies. Intact native prairies of any kind have become quite rare in the state, and the dry sandy prairies inhabited by C. obtusata are among the rarest. Only a few such prairies in central and northwestern Minnesota are known to support this species. Even in prairies where C. obtusata is found, its population numbers are often precariously low. Management of surviving habitat fragments requires an active program of prescribed fire, invasive species monitoring, and control of motorized vehicle access. A commitment to management of this intensity has not yet materialized on a broad scale, which adds another degree of uncertainty to the future of this species in Minnesota. Carex obtusata was listed as a special concern species in the state in 1984.
Carex obtusata is a perennial sedge that grows 10-20 cm (4-8 in.) high. The stems have red-brown or red-purple bases and arise singly from nodes spaced along a long, horizontal rhizome rather than from a dense clump. The leaves are 0.5-1.5 mm (0.02-0.06 in.) wide and have hairless surfaces. The inflorescence consists of a single spike with fewer than 10 flowers. The perigynia (the membranous covering of the seed) is smooth, brown to reddish black at maturity, broadly elliptical to obovate in outline, and round or nearly round in cross-section. It has an abrupt beak at the apex. Of the 150+ species of Carex in Minnesota, very few have stems that arise singly from a horizontal rhizome and have only one spike. Among those few, only C. obtusata has brown or blackish perigynia and stems with dark-colored bases.
Carex obtusata inhabits native grasslands that have developed on dry, sandy or gravelly soil. These are usually found on sandy alluvial terraces, sandy outwash plains, or beach ridges of Glacial Lake Agassiz. The nutrient poor soils usually support a sparse cover of vegetation with patches of bare ground between clump-forming grasses.
Biology / Life History
We have very little specific information about the biology of C. obtusata. Its structure reveals it to be a perennial that produces flowers that are pollinated by wind, and small hard seeds (achenes) that are dispersed by gravity and perhaps animals. Given the fire-maintained nature of prairie habitats, it is reasonable to assume that C. obtusata is "fire adapted". It might also be assumed that the stiff, narrow leaves and tough rhizomes are perhaps adaptations to survive in droughty soils. Indeed, observations have shown that C. obtusata is very tolerant of drought. Although it is clearly a tough and durable survivor, it rarely dominates extensive portions of its habitat in Minnesota. That role is usually performed by clump-forming grasses such as Schizachyrium scoparium var. scoparium (little bluestem), Andropogon gerardii (big bluestem), and Koeleria macrantha (junegrass). These are deep-rooted grasses that usually form scattered clumps, leaving open ground between them for mobile, shallow-rooted sedges such as C. obtusata.
Conservation / Management
Open and undeveloped prairies, especially prairies with sandy soil, seem to be magnets for OHVs (off-highway vehicles). This is a class of heavy recreational vehicle that can be very destructive to fragile soils and native vegetation. Their use can lead to soil erosion and the invasion of non-native species. Exotic sod-forming grasses such as Bromus inermis (smooth brome), Elymus repens (quackgrass), and Poa pratensis (Kentucky bluegrass) are especially damaging; they must be monitored and carefully controlled.
Conservation Efforts in Minnesota
No known conservation efforts have been undertaken specifically on behalf of C. obtusata although several populations are known to occur on public lands including Agassiz Dunes and Felton Prairie Scientific and Natural Areas; Crane Meadows, Enerson, Huntly, Pembina, Thief Lake, and Twin Lake Wildlife Management Areas; and Lake Bronson and Old Mill State Parks.
Murray, D. F. 2002. Carex sect. Obtusatae. Page 555 in Flora of North America Editorial Committee, editors. Flora of North America north of Mexico. Volume 23. Oxford University Press, New York, New York.