Spikes:

Separate staminate (male) and pistillate (female) spikes, with a single staminate spike up to 1½ inches long at the tip of the stem. Below the staminate spike are 1 to 3 pistillate spikes, ¼ to 1½ inches (.7 to 4 cm) long, widely spaced, the uppermost stalkless or nearly so, the lowest usually on an erect stalk. At the base of the lowest pistillate stalk is an erect, leaf-like bract that does not overtop the terminal spike and has a sheath up to 2 inches (5 cm) long.

Leaves and stems:

Leaves are alternate, number 3 to 5 all on the lower stem, dark green or yellow-green, erect to ascending, 1.5 to 4.5 mm wide, and shorter than the flowering stem. Stem leaf sheaths are white to yellowish on the front, concave to V-shaped at the tip and tightly wrap the stem. The ligule (membrane where the leaf joins the sheath) is 1 to 2 times as long as wide, rounded to blunt across the tip.

Bases are wrapped in a brown or sometimes purple-tinged sheath that is not much fibrous. Stems are single or a few together, slender, mostly erect, 3-sided, smooth except near the spikes, elongating up to 24 inches at maturity and longer than the leaves. Plants form loose colonies from long rhizomes.

Fruit:

Fruit develops in late spring to early summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Pistillate spikes each contain 6 to 20 fruits that are mostly ascending, overlapping on the stalk, usually in 2 to 4 columns, the lowest perigynia often loosely arranged especially on the lowest spike, and the mature spike 3.5 to 5.5 mm diameter.

Pistillate scales are oval to egg-shaped, blunt to pointed at the tip, white to dark chestnut or purplish-brown along the edges with a broad green midrib that may extend to a an awn shorter than the scale body, the body half to ¾ as long as the perigynia. Perigynia are 2.5 to 4 mm long, 1.2 to 1.8 mm wide, 4 to 13-veined (best seen when dry), hairless, green, loosely wrapping the achene, nearly round in cross-section, usually tapering to a toothless, beakless tip, sometimes with an obscure, minute, bent beak. Achenes are 2 to 2.5 mm long, 1.2 to 1.6 mm wide, 3-sided in cross-section, reddish to dark brown at maturity.

Notes:

Carex tetanica is a common sedge in Minnesota, found in more than half the state. most often in the moist to wet soils of sedge meadows, prairie swales, calcareous fens, seeps, and swamp and marsh margins, only occasionally in drier grasslands or 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 tetanica is in the Paniceae section; some of its common traits are: clump forming or not, rhizomatous, hairless leaves, basal sheaths brown or red-purple, sheaths sometimes fibrous, 2 to 4 spikes, terminal spike all-staminate, lateral spikes all-pistillate and stalked, leaf-like bract subtending the lowest pistillate spike with a sheath more than 4 mm long, perigynia ascending to spreading, hairless, weakly 3-sided to round in cross-section, beaked or not, at least slightly inflated, achenes 3-sided in cross-section.

Carex tetanica is distinguished from all other Minnesota sedges by the combination of: not clump-forming, long-rhizomatous forming loose colonies; largest leaves 3 to 4.5 mm wide; a single terminal staminate spike; 1 to 3 pistillate spikes each containing 6 to 20 fruits, the upper spike stalkless and the lowest usually on an erect stalk, lowest perigynia on the largest spike often loosely arranged; perigynia 2.5 to 4 mm long, loosely wrapping the achene, usually tapering to a toothless, beakless tip, sometimes with an obscure, minute, bent beak; achenes 3-sided, up to 1.6 mm wide.

Carex tetanica most closely resembles Carex meadii and it can be very difficult to distinguish them. Per Flora of North America: “Separating Carex meadii and C. tetanica can be problematic, particularly in the Great Lakes region where they seem to intergrade with each other.” Indeed. The general consensus across its range is C. tetanica is more likely to be found in wetter habitats than C. meadii, its spikes tend to be narrower (3.5 to 5.5 mm vs. 4.5 to 7 mm), the perigynia more loosely arranged in fewer columns (2 to 2 vs. up to 6), its perigynia most often tapering to a toothless, beakless tip (vs. a more distinct, minute bent beak), its achenes narrower (usually under 1.5 mm wide vs. usually over 1.5 mm wide), its leaves more yellow-green, the widest 3 to 4.5 mm wide (vs. blue-green or gray-green, 4 to 7 mm wide), and ligules mostly longer than wide (vs. mostly wider than long). Note there is overlap on many of these traits, but the most consistent differences I saw in herbarium specimens were C. tetanica in relatively wet habitats, the short, bent beak on few perigynia, and achenes not more than ~1.5 mm wide.