Rare Species Guide

  Basis for Listing

Carex conjuncta (jointed sedge) is an inhabitant of floodplain forests of central and eastern U.S., reaching the northern periphery of its range in Minnesota. It seems to be fairly common in the center of its range in Missouri and Illinois but rare or local in Minnesota and portions of adjacent Wisconsin and northern Iowa.

In Minnesota, to date, it has been found only along a relatively short stretch of the Cannon River (Rice and Dakota counties) and at one site along Dodge Center Creek (Dodge County). The Dodge Center Creek population could not be found in recent searches and may or may not still exist. It was always very small and was perhaps transient. Carex conjuncta was listed as a threatened species in Minnesota in 1984.

  Description

Sedges are grass-like perennial herbs that can be easily identified to the genus Carex by their three-ranked leaves, closed sheaths, and triangular (only occasionally round), mostly solid stems with a 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 conjuncta has numerous spikes forming an interrupted inflorescence; some or all spikes have terminal staminate flowers. The perigynia are glabrous, ovate, 3.3-4.7 mm (0.13-0.19 in.) long, 1.5-2.4 mm (0.06-0.09 in.) wide, with a spongy base and a serrulate beak. The rhizomes are short resulting in a clumped growth form. The inner band of the leaf sheath is cross-puckered and covered with tiny purple dots. Most of these characters, except the purple dots and perigynia dimensions, are shared with the otherwise similar C. alopecoidea (foxtail sedge) and C. stipata var. stipata (awl-fruited sedge).

Technical Description: Culms cespitose, to 90 cm (35 in.) long, wing-margined, weak, flattened in pressed specimens. Rhizomes to about 3 cm (1 in.) long. Leaves to 8 mm (0.3 in.) wide; ventral surface of sheaths with transverse wrinkles, spotted with small purplish dots (especially near summit); basal sheaths disintegrating into coarse brown fibers and persisting at base of culm and on rhizomes. Inflorescence 4.0—7.0 cm 1.6—2.8 in.) long; compound, with a few to several short side branches. Spikes numerous, sessile, androgynous; bracts setaceous. Pistillate scales about two-thirds to fully as long as the perigynia; apex acuminate or short-awned. Perigynia glabrous, ovate, 3.3--4.7 mm (0.13—0.19 in.) long, 1.5--2.4 mm (0.06—0.09) wide, distinctly veined dorsally, veinless or indistinctly veined ventrally; base spongy or pulpy; apex tapered or slightly contracted to a bidentate serrulate beak 1--1.8 mm (0.04—0.07 in.) long; beak shorter than the body. Achenes biconvex; style deciduous. Maturing June through July.

  Habitat

The Minnesota populations occur in mature floodplain forests under a canopy of Ulmus americana (American elm), Juglans nigra (black walnut), and Acer saccharinum (silver maple). This habitat type is usually flooded in the spring and may remain wet or moist throughout the summer. Carex conjuncta occurs along with other rare sedges such as C. davisii (Davis' sedge) and C. grayi (Gray's sedge).

  Biology / Life History

Carex conjuncta is a perennial sedge. The flowers are wind-pollinated and it reproduces only by seed. Dispersal mechanisms are not known, but it is likely that perigynia and possibly rhizomes are transported on spring floodwaters.

  Conservation / Management

In Minnesota, C. conjuncta is known to occur only in a floodplain forest along a small stretch of the Cannon River and in a similar habitat at a single site along Dodge Center Creek, both in the southeastern corner of the state (Big Woods and Oak Savanna subsections). Although uncertain, it is believed this is the only habitat type in which the species might occur in Minnesota. These sites should be monitored to ensure invasive species that could threaten the ecological integrity of the habitats do not become established.

  Best Time to Search

The best time to search for Carex conjuncta is in July when the species is in fruit.

  Conservation Efforts in Minnesota

The DNR's Minnesota Biological Survey has been completed within the likely range of the species in the state.

  Authors/Revisions

Welby R. Smith (MNDNR), 2021

(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.

Gilley, C. L. 1946. The Cyperaceae of Iowa. Iowa State College Journal of Science 21:55-151.

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., and G. B. Ownbey. 1984. Annotated List of Minnesota Carices, with phytogeographical and ecological notes. Rhodora 86(846): 151-231.