Rare Species Guide

  Basis for Listing

Carex formosa (handsome sedge) has a very restricted and discontinuous range and is considered rare or local in most of the states and provinces where it occurs. In Minnesota, it is known by historical records to have occurred at four locations in forests along the Mississippi River in the Twin Cities metropolitan area (Minnesota and Northeast Iowa Morainal Section), but as of 2018 only a handful of plants at one site have been relocated. There is one diffuse population occurring along the Zumbro River in southeastern Minnesota (Rochester Plateau Subsection) and a cluster of three populations in northwestern Minnesota (Aspen Parklands and Hardwood Hills subsections). These are quite separate from known populations in Wisconsin and North Dakota (Wheeler 1983).

The extant populations occur in fragile woodland habitats that cannot sustain heavy use. Because these habitats are also prime locations for residential development, timber harvest, and livestock grazing, the few remaining populations are particularly vulnerable. Given its extreme rarity and vulnerability, C. formosa was listed as an endangered species in Minnesota in 1996.

  Description

Carex formosa is a forest sedge with relatively broad leaves, reddish basal sheaths, and drooping spikes. There are two features which, in combination, set it apart from similar sedges. First, the presence of hairs on the leaves, especially the leaf sheaths. Secondly, the gynecandrous arrangement of flowers on the lateral spikes. The term gynecandrous means the female flowers are above and the male flowers are below. The female flowers are identified as having perigynia. The male flowers are seen as empty scales wrapped tightly around the peduncle. This arrangement is significant only when applied to the lateral spikes. 

Technical description: Culms cespitose, to 85 cm long. Rhizomes to about 3 cm long or not apparent. Leaves to 8 mm wide (the widest per specimen at least 4 mm), typically not surpassing the culms in length; sheaths and lower surface of blades pubescent; basal sheaths dark red or reddish black, ladder-fibrillose. Terminal spike gynecandrous; the lower 2/3 staminate, the upper 1/3 pistillate. Lateral spikes 3--4 per culm, staminate at the base, pistillate towards the apex, 1.3--3 cm long, with 8--35 perigynia each; peduncles as long or longer than the spikes, drooping. Pistillate scales 1/2--3/4 as long as the perigynia; apex acute or with awn no more than 1 mm long. Perigynia glabrous, ellipsoid to oblong-ellipsoid, 3.5--4.7 mm long, 1.6--2.2 mm wide, with 2 distinct veins and a few to several obscure veins; beak abrupt, tubular, 0.3--0.5 mm long. Achenes distinctly trigonous, 2.2--2.8 mm long; style deciduous. Maturing mid-May to mid-June.

  Habitat

In Minnesota, populations of C. formosa were first discovered on forested slopes along the Mississippi River in Ramsey and Hennepin counties (Wheeler 1981), though habitat and locational details are lacking. The population in southeastern Minnesota is in a fire-excluded forest on low river valley slopes dominated by Acer saccharum (sugar maple) and Tilia americana (basswood); a community classified as southern mesic maple-basswood forest. The populations in northwestern Minnesota occur in flat terrain in fire-dependent forests of Populus tremuloides (quaking aspen) and Quercus macrocarpa (bur oak); a community classified as northwestern mesic aspen-oak woodland. Soils at all sites are mesic loams and developed in areas where calcareous glacial material is often a component of soils. Although extremely rare, C. formosa may be locally abundant at these sites.

  Biology / Life History

Carex formosa is a native perennial that reproduces only by seeds. Flowers are wind-pollinated. The stems grow vertically and continue to elongate throughout the season. When the perigynia become mature (mid-summer), the culms lie flat on the ground, dispersing the seeds the length of the stems (no more than about 1 meter [3 ft.]). How seeds might disperse over greater distances is unknown but likely involves small mammals or ground foraging birds. It is not known to be a disturbance-dependent species.

  Conservation / Management

The extant population of C. formosa in southeastern Minnesota occurs discontinuously along about a mile of forested river valley. This habitat type is particularly vulnerable to housing developments, road building, and other land conversion activities. Direct damage to the habitat is one consequence, but activities higher up the slopes or on level land above the slopes could lead to erosion and indirect changes to the habitat. Furthermore, any habitat changes that alter the specific light, temperature, and moisture regime at the level of the forest floor would almost certainly alter the competitive balance of the ground flora and be harmful to C. formosa. Such changes would likely result from alterations to the tree canopy and livestock grazing. The loss of single canopy trees through such natural processes as windstorms and lightning strikes would be easily and quickly replaced through natural processes and would not constitute a significant degradation of the habitat. However, loss of more than isolated single trees would likely change the environmental conditions on the forest floor and result in the invasion of non-native species, such as Rhamnus cathartica (common buckthorn) and Alliaria petiolata (garlic mustard). This would constitute a serious threat. Control of invasive species, should they become established, is essential, but chemical control has a great risk of unintended consequences and should be avoided.

Populations in northwestern Minnesota are on level terrain rather than the hilly terrain of the southeast. They survive in remnants of early successional forested habitats in a landscape that is currently dominated by agricultural activity. The history of these forests is unclear, but they were likely subjected to periodic wildfire in the past (prior to agriculture being introduced into the region). However, it is unclear if C. formosa survived such fires in situ or was able to recolonize after habitats recovered from fire. In either case it would be unwise to assume that the small isolated fragments of surviving habitat can be managed with fire (or clearcutting) and get positive results. Livestock grazing is another modern activity that does not mimic the effects of free roaming native ungulates that might have originally occurred in the area. 

  Best Time to Search

The best time to search for Carex formosa is in June and July, when reproductive structures (perigynia) are present.

  Conservation Efforts in Minnesota

One site of C. formosa occurs in a county park, but management plans that address the ecological needs of this rare plant are needed.

  Authors/Revisions

Welby R. Smith (MNDNR), 2020

(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.

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. 1988. Natural Communities and Rare Species of Olmsted County. Biological Report No. 51. 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. 1983. Carex formosa in North Dakota. The Michigan Botanist 22:162.

Wisconsin Department of Natural Resources, Bureau of Endangered Resources. 1993. Guide to Wisconsin's Endangered and Threatened Plants. Wisconsin Department of Natural Resources PUBL-ER-067, Madison, Wisconsin. 128 pp.