Spikes:

5 to 12 spikes each 12 to 28 mm (to 1+ inch) long, all at the tip of the stem, overlapping but not tightly crowded, the inflorescence (group of spikes) erect or slightly nodding and 2 to 3½ inches long. All spikes are stalkless, erect to ascending, narrowly elliptic to spindle-shaped, tapering to a point at both ends, with staminate (male) flowers at the base and pistillate (female) flowers at the tip (gynecandrous). At the base of each spike is a scale-like bract.

Leaves and stems:

Leaves are all alternate, spiraling the stem with 3 leaves in a cycle (3-ranked), appearing as 3 columns when viewed from the top. Leaves are hairless, flat, up to 10 inches long, 3 to 4 mm wide, bright green, rough along the edges especially near the tip. Flowering stems have 7 to 12 leaves on the lower half, vegetative stems are even leafier and evenly distributed along the entire length.

Stem leaf sheaths tightly wrap the stem and are mostly green nearly to the tip, the narrow, whitish translucent band across the tip U- to V-shaped. The ligule (membrane where the leaf joins the sheath) is about as long as wide. Bases are wrapped in a brown sheath that may be somewhat fibrous, with old leaves often persisting to the next season. Stems are hairless, mostly erect, 3-sided in cross-section, mostly smooth except just below the spikes. Stems may elongate to 40 inches at maturity and are longer than the leaves, but leaves of vegetative stems may surpass the spikes. Plants are clump forming and may form loose colonies of flowering and vegetative shoots.

Fruit:

Fruit develops starting in early summer, the spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Perigynia are appressed and crowded on the spike. Each spike contains numerous fruits.

Pistillate scales are lance-elliptic, translucent, whitish to brown-tinged with a green or pale midrib, blunt to pointed at the tip, 4 to 5 mm long, much shorter than the perigynia. Perigynia are 6 to 9 mm long, 2 to 2.5 mm wide, greenish to straw-colored to light reddish-brown at maturity, hairless, distinctly 5 to 7-veined on the front and 3 to 7-veined on the back, flattened, not inflated, the body narrowly lance-elliptic, tapered at the base, long tapered to a beak at the tip, and has a translucent, papery wing .2 to .4 mm wide around the edges that narrows significantly on the lower half and is minutely toothed or fringed at least near the beak. Achenes are lens-shaped, brown, 2 to 2.7 mm long, .8 to .9 mm wide, oblong; the distance from the tip of the achene to the tip of the beak is 3.1 to 4.5 mm.

Notes:

Carex muskingumensis is an uncommon sedge of floodplain forest, sometimes vernal pools, and reaches the northwestern edge of its range in Minnesota. First recorded in Chisago county in 1885, it was not recorded again for nearly 100 years, when it was found in Mississippi River floodplains from Goodhue County south. According to the DNR, the lock and dam system constructed on the Mississippi during the 1930s has been detrimental to many species dependent on the normal, cyclic fluctuating water levels that are characteristic of floodplains. It was listed as a Special Concern species in 2013.

Carex is a large genus, with over 600 species in North America and 150+ in Minnesota alone. They are grouped into sections, the species in each group having common traits. Carex muskingumensis is a member of the Ovales section, a notoriously difficult group. Some common traits are: usually clump forming, basal sheaths brown and somewhat fibrous, leaves V-shaped when young; 2 to 20 stalkless spikes all at the stem tip and crowded or not, spikes usually all pistillate at the tip and staminate at the base (gynecandrous), lowest bracts scale-like usually with a bristle tip, pistillate scales blunt to pointed at the tip and sometimes awned; perigynia erect to spreading, hairless, veinless to conspicuously veined on one or both surfaces, flat, beaked, usually with a translucent, papery wing; achenes lens-shaped.

Some traits to look at in Ovales are whether spikes are all crowded at the tip or more loosely arranged, whether the inflorescence is nodding or mostly erect, the shape of the spike (round vs. elliptic vs. club-shaped), the size and shape of the perigynia particularly the body (e.g. round vs. elliptic), the width of the wing and whether it extends all the way to the base, whether there are distinct veins on one or both sides of the perigynia, the length of the pistillate scale relative to the perigynia, the shape of the achene, leaf width, and whether sheaths are papillose, but strong magnification (30x or more) is required to see this. Habitat can also be a factor, and a metric scale is essential since fractions of millimeters make a difference.

Carex muskingumensis may be the easiest of the Minnesota Ovales sedges to identify. The leafy stems that are strongly 3-ranked, the long (to 1+ inch) slender spikes tapering to a point at both ends, and floodplain forest habitat is unique not just for Ovales, but across other MN sedges as well. When fertile shoots are not present (or yet developed) the leafy stems may resemble Carex cristatella, C. tribuloides or C. projecta, all of which have sheaths that are somewhat loose and winged, and widest leaves at least 4 mm long, where C. muskingumensis sheaths are tight and not winged, and widest leaves are not more than 4 mm.