Spikes:

3 to 7 spikes each 7 to 15 mm (to ~½ inch) long, all at the tip of the stem, usually overlapping but not crowded, the inflorescence (group of spikes) erect or slightly nodding and about 1 to 1½ inches long. All spikes are stalkless, erect to ascending, rounded at the tip, usually tapering at the base, round to oval to somewhat club-shaped in outline, with staminate (male) flowers at the base and pistillate (female) flowers at the tip (gynecandrous). At the base of the lowest spike is a scale-like bract with a bristle-like tip that may be longer than the spike but does not usually overtop the terminal spike.

Leaves and stems:

Leaves are alternate with 3 to 6 leaves on the lower third of the stem, 1.5 to 4 mm wide, shorter than the flowering stem, flat, hairless, rough along the edges especially near the tip. Stem leaf sheaths tightly wrap the stem and are mostly green nearly to the tip, the whitish translucent tip extending up to 2 mm above the leaf base and is U- to V-shaped across the top edge. 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. Not all plants produce flowering stems. Plants are usually densely clump forming. At maturity, the whole plant may flatten out in a radiating pattern.

Fruit:

Fruit develops in late spring to mid summer, the spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Perigynia are ascending to somewhat spreading and crowded to somewhat loose on the spike. Each spike contains 10 to 40 fruits.

Pistillate scales are lance to egg-shaped, translucent, whitish to golden brown tinged with a green midrib drying to brown, blunt to pointed at the tip, 2.6 to 4.3 mm long, somewhat shorter than to about as long as the perigynia. Perigynia are 3 to 5 mm long, 2 to 3.3 mm wide, greenish to reddish-brown at maturity, hairless, distinctly veined on the front, veinless or obscurely veined on the back, flattened, not inflated, the body nearly round, rounded at the base, abruptly tapered to a beak .8 to 1.2 mm long, and has a translucent, papery wing .3 to .8 mm wide around the edges all the way to the base and is often minutely toothed or fringed at least near the beak. Achenes are lens-shaped, brown, 1.5 to 2.2 mm long, 1.2 to 1.8 mm wide, broadly egg-shaped to nearly round; the distance from the tip of the achene to the tip of the beak is 1.5 to 2.4 mm.

Notes:

Carex brevior is a common sedge of dry, sandy or rocky soils, found in prairies, savannas, rock outcrops, dunes and grassy slopes, rarely in open woods.

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 brevior 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 brevior is distinguished from other Minnesota Ovales species by 3 to 7 spikes tapered at the base, the terminal spike with a distinct staminate portion, spikes not usually crowded together; perigynia 3 to 5 mm long (usually 4 mm or less), the body nearly round, distinctly veined only on one side and winged to the base, the wing may be minutely toothed or fringed near the beak but is not jagged. The distance from the tip of the achene to the tip of the beak is 1.5 to 2.4 mm.

Carex brevior is most similar to C. bicknellii, C. merritt-fernaldii, and C. molesta, all of which have somewhat larger perigynia, though there is overlap. C. bicknellii is also strongly veined on both sides of the perigynia; it and C. merritt-fernaldii both have papillose sheaths, which C. brevior lacks, and more irregular wings that are commonly a bit jagged on the upper half or so. C. molesta spikes are rounded at the base (very few staminate flowers) and more tightly crowded at the stem tip, its perigynia bodies more oval, and achenes are oblong-elliptic, distinctly longer than wide.

As a side note, when I first undertook the Ovales group everything looked like C. brevior to me. :-) It takes a bit of study to pick up the nuances of this difficult group, but it can be done. Patience is a virtue.