Spikes:

3 to 10 spikes each 6 to 16 mm (to 2/3 inch) long, all at the tip of the stem, overlapping, the spikes tightly crowded or overlapping but distinctly separated, or the uppermost crowded and the lower more separated, the inflorescence ;(group of spikes) erect to arching and ¾ to 2+ inches long. All spikes are stalkless, erect to ascending, tapering to rounded at the tip, usually tapering at the base, oval-elliptic to club-shaped or occasionally nearly round 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 and sometimes overtops the terminal spike.

Leaves and stems:

Leaves are alternate with 2 to 6 leaves on the lower half of the stem, up to 20 inches long, 1.5 to 3 mm wide, flat, hairless, rough along the midvein and edges, usually shorter than the flowering stem. Stem leaf sheaths tightly wrap the stem and are mostly green nearly to the tip, the whitish translucent tip extends 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 or longer than 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 about 40 inches at maturity and are longer than the leaves. Plants are clump forming from a mix of vegetative and flowering stems.

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 mostly ascending, rarely spreading, and are crowded on the spike. Each spike contains numerous fruits.

Pistillate scales are lance to egg-shaped, translucent light brown-tinged with a green or pale midrib drying to pale brown, tapering to a sharply pointed tip, somewhat shorter and narrower than the perigynia. Perigynia are 4 to 6.5 mm long, 1.2 to 2 mm wide, mostly golden brown at maturity, hairless, 5-veined on each side or more obscurely veined on the back, flattened, not inflated, the body lance-elliptic, tapering at the base, long-tapered to the beak, and has a wing .2 to .6 mm wide around the edges that abruptly narrows in about the middle of the perigynia body. Achenes are lens-shaped, brown at maturity, 1.3 to 1.7 mm long, .7 to .9 mm wide, narrowly egg-shaped to elliptic, longer than wide; the distance from the tip of the achene to the tip of the beak is 2.2 to 4.8 mm.

Notes:

Carex scoparia is a common sedge in moist to wet open places in much of the state, more commonly from the Twin Cities north. Habitats include sandy or gravelly pond and lake shores, river banks, moist meadows, swales and wet ditches, less often in the margins of swamps, marshes and bogs, in rock outcrops, and in the crevices and ledges of bluffs and cliffs.

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 scoparia 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 scoparia is somewhat variable, but may be distinguished from other Minnesota Ovales species by widest leaves usually less than 3 mm; 3 to 10 spikes either all crowded together at the stem tip or overlapping but distinctly separated, the inflorescence erect to arching and up to 2+ inches long; spikes mostly elliptic in shape, tapered at both ends or rounded at the tip; perigynia 4 to 6.5 mm long and 1.2  to 2 mm wide, 5-veined on both sides or obscurely so on the back, not winged to the base. The distance from the tip of the achene to the tip of the beak is 2.2 to 4.8 mm. Fruiting stems typically rise well above the leaves and it's found in a variety of moist to wet soils. Of note is we've encountered at least two populations with particularly large spikes of maybe twice as many perigynia as normal; those spikes were nearly globular.

There are currently 2 recognized varieties of C. scoparia: var. tessellata, endemic to eastern Maine, has a compact inflorescence, darker scales and perigynia up to 2.6 times as long as wide; var. scoparia, common across North America including Minnesota, has a compact or more loosely arranged inflorescence, golden or pale brown scales and perigynia 2.8 or more times as long as wide. Some references consider the compact vs. looser arrangement of the spikes as separate varieties, but both may be in the same population if not on the same plant, so that distinction doesn't hold water.

Carex scoparia is most similar to C. crawfordii, with which it may grow, and which has smaller perigynia (3 to 4.3 mm long and not more than 1.2 mm wide) and fruiting stems are rarely more than about 24 inches tall.

While researching C. crawfordii I learned that it and several other North American Ovales have been introduced to Europe and parts of Asia and are becoming invasive there. C. scoparia was first recorded in Slovakia in 1982 and more recently in several other European countries; its rapid expansion in Austria has been cause for concern. It is thought to have been introduced in Belgium as a contaminant in coconut matting. It has also been naturalized in New Zealand since 1948.