Carex davisii Schwein. & Torr.
Click to enlarge
Basis for Listing
Carex davisii is a typical sedge of forested floodplains and swamps in the Midwest and east-central states, but it is quite rare in the Mississippi River drainage north of Illinois. Prior to 1979, it was known in Minnesota only by a herbarium specimen collected in 1918 in the Zumbro River bottoms, Wabasha County. Since 1979, C. davisii has been located in a few additional sites in southeastern Minnesota. However, the construction of locks and dams early in the 20th Century resulted in a major loss of floodplain forest habitat along the Mississippi River. Compounding that loss was the subsequent loss of forest cover along major tributaries such as the Root, Cannon, and Zumbro rivers. These more recent losses were primarily from agricultural expansion, road building, residential development, and the invasion of non-native species. All considered, the loss and degradation of floodplain forests in southeastern Minnesota has been devastating to C. davisii and a number of other highly specialized species. For these reasons, C. davisii was listed as a threatened species in Minnesota in 1984.
Sedges are grass-like, perennial herbs that can be easily identified as a group 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. Carex davisii can sometimes be confused with C. formosa (handsome sedge). Both species have terminal spikes with staminate (male) and pistillate (female) flowers as well as pubescent leaves, at least on the underside. Leaf sheaths of both species are strongly reddened at the base. Carex davisii can be distinguished by its lateral spikes, which are entirely pistillate, and by its scales, which have long, narrow tips that are as long or longer than the perigynia. Unlike related species, the perigynia is dull orange at maturity. The fruit (achene) is concavely trigonous. Leaves and culms arise from a tufted (cespitose) base (Gleason and Cronquist 1991).
All Minnesota C. davisii populations occur in mature alluvial forests associated with major river valleys of the Mississippi River drainage in the southeastern corner of the state. Major canopy trees in floodplain forest habitat supporting C. davisii include Quercus bicolor (swamp white oak), Fraxinus pennsylvanica (green ash), Acer saccharinum (silver maple), Ulmus thomasii (rock elm), Celtis occidentalis (hackberry), Tilia americana, (basswood) and Populus deltoides (cottonwood). This shaded habitat is occasionally inundated by spring floods, but is dry or moist the rest of the year. Carex davisii seems to be restricted to floodplain zones that are inundated by only the highest flood events. These less-active floodplain conditions are more typical of major tributary river systems such the Root, Cannon, and Zumbro rivers, and zones that support Q. bicolor along the Mississippi River. Carex davisii has not been recorded in areas that remain inundated for weeks at a time, a more typical condition for most of the silver maple floodplain forest remaining along the Mississippi River. Collection records indicate that individuals are often scattered in each population and few in number.
Biology / Life History
Carex davisii is a perennial sedge that is wind-pollinated and reproduces only by seed. It drops its perigynia sooner than many of the Carex species that share its habitat. Perigynia are somewhat inflated, presumably an adaptation for dispersal on floodwaters.
Conservation / Management
It is clear that the dramatic change in the character of the Mississippi River floodplain following the construction of locks and dams early in the 20th Century has had a major impact on the habitat of this rare plant. Land clearing for agriculture has also caused major losses. Furthermore, the health of floodplain forests is being compromised by establishment of dense colonies of Phalaris arundinacea (reed canary grass), which interferes with forest regeneration. High quality native habitats of C. davisii have now become so limited that immediate measures may be necessary to prevent further losses. Agricultural expansion and residential and commercial development may still pose serious threats to the species. Clearcutting of forests in the vicinity of known locations should be avoided.
Conservation Efforts in Minnesota
The Minnesota DNR County Biological Survey has been completed in the likely range of C. davisii in the state. Most populations are on private land and considered vulnerable to land use changes.
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.
Ball, P. W., and D. J. White. 1982. Atlas of the Rare Vascular Plants of Ontario.
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.
Ownbey, G. B., and T. Morley. 1991. Vascular plants of Minnesota: a checklist and atlas. University of Minnesota Press, Minneapolis, Minnesota. 320 pp.
Wheeler, G. A. 1981. A study of the genus Carex in Minnesota. Dissertation, University of Minnesota, St. Paul, Minnesota. 501 pp.
Wheeler, G. A., and G. B. Ownbey. 1984. Annotated List of Minnesota Carices, with phytogeographical and ecological notes. Rhodora 86:151-231.