Spikes:

Several to numerous small spikes, all essentially alike, stalkless or nearly so, erect to ascending, usually all overlapping and crowded at the tip of the stem, the lower sometimes slightly separated, the group of spikes (inflorescence) straight and 1 to 3 inches long, the lowest spike(s) often branched. Spikes mostly have a few staminate (male) flowers at the tip and pistillate (female) flowers below (androgynous) but occasionally are all staminate or all pistillate. At the base of a lateral spike is an awned, scale-like bract, the lowest as long as or somewhat longer than the attending spike but much shorter than the inflorescence.

Leaves and stems:

Leaves are basal and alternate with 4 or 5 leaves on the lower ¼ of the stem, 1 to 3 mm wide, up to 12 inches long and mostly not overtopping the flowering stems. Stem leaf sheaths tightly wrap the stem and are translucent whitish, straight to slightly concave or convex at the tip, strongly dotted on the front, at least some of the dots coppery red, otherwise white, and the tip of the sheath extending .4 to 4+ mm above the leaf base. The ligule (membrane where the leaf joins the sheath) is as long as or longer than wide. Leaves are hairless and rough along the edges, V-shaped in cross-section when young, and mostly erect but arching at the tip.

Bases are wrapped in a brown sheath that is not fibrous. Stems are slender, 3-sided, rough textured on the angles, erect to ascending, elongating up to about 3 feet at maturity and usually longer than the leaves. Not all plants produce flowering stems. Plants form loose to dense clumps from short rhizomes.

Fruit:

Fruit develops in late spring through early summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Spikes usually contain a few to several fruits that are ascending to spreading and overlapping on the stalk.

Pistillate scales are broadly lance-shaped, yellowish to brown with whitish edging and a green midrib drying to light brown, usually tapering to a pointed tip, are about as long and wide as the perigynia or nearly so, and mostly concealing it. Perigynia are 2 to 3 mm long, 1 to 1.4 mm wide, shiny dark olive to dark chestnut brown at maturity, strongly 4 to 6-veined on the outer (front) surface with a narrow stripe down the center all the way to the base (bordered by the raised veins), the inner (back) surface somewhat flattened and weakly 2 to 4-veined near the base, hairless but with minute serrations along the tip edges, firm, thick walled and tightly wrapping the achene, the body oval to egg-shaped, the base rounded to straight across and often abruptly narrowed, the tip tapered to a green to brown, toothed beak up to 1 mm long. Achenes are 1.4 to 1.7 mm long, .7 to 1 mm wide, flattened lens-shaped, tapering to a stalk-like base, often abruptly so.

Notes:

Carex diandra is a circumboreal species found in a variety of wet places. In Minnesota it is most abundant in peatland fens and the floating mats of alkaline lakes, less often in wet ditches, wet meadows, and bog edges.

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 diandra is in the Heleoglochin section; some of its common traits are: growing in (usually) dense clumps, slender stems 1mm wide or less at the tip, basal sheaths brown, leaves flat or V-shaped in cross-section when young, leaves hairless, sheaths coppery to red dotted, lowest bracts scale-like and awned, numerous spikes often branched, terminal spike usually with staminate flowers at the tip (androgynous), lateral spikes androgynous or all-pistillate, perigynia flattened in cross-section, strongly veined on the front, thick-walled or leathery, abruptly tapered to a stalk-like base (stipe), beaked with 2 teeth at the tip, flattened lens-shaped achenes. Members of the Heleoglochin section somewhat resemble those of the Multiflorae and Vulpinae sections, both of which (usually) lack the red dotted sheaths, and have perigynia that are more spongy and not thick-walled or leathery.

Carex diandra is distinguished from other sedges by the combination of: clump forming, widest leaves 3mm wide or less, stem leaf sheaths white and strongly dotted with coppery red and/or white dots, the tip of the sheath extended up to 4+mm above the leaf base, most or all spikes crowded with a few staminate flowers at the tip (androgynous), the perigynia 3mm long or less, shiny, dark olive or dark chestnut brown at maturity, distinctly nerved on the front with a somewhat paler stripe down the center all the way to the base. It most closely resembles Carex prairea, which has sheaths that are solid coppery colored especially at the tip, spikes that are typically more widely separated from each other, the inflorescence often arching rather than straight, and requires calcareous soils where C. diandra does not. Other species with a somewhat similar inflorescence are Carex siccata, Carex sartwellii, and members of the Divisae section, all of which are rhizomatous and not clump-forming, lack the dotted stem leaf sheaths, and do not have thick-walled perigynia.