Spikes:

Separate staminate (male) and pistillate (female) spikes, with 1 to 5 staminate spikes to 2½+ inches long at the tip of the stem, sometimes with a few pistillate flowers at the tip (gynecandrous) or the base (androgynous) or otherwise mixed. Well-separated from the staminate spikes are 2 to 5 pistillate spikes, occasionally with a few staminate flowers at the tip, each up to 4 inches long, cylindric, 5 to 15 mm (to ~½ inch) in diameter, short-stalked to stalkless, erect to ascending, the longer spikes sometimes nodding. At the base of each pistillate spike is a leaf-like bract; that of the lowest spike is up to 20+ inches long, over-topping the terminal spike.

Leaves and stems:

Leaves are basal and alternate, flat or folded (V-shaped), the largest leaves 4 to 12 mm wide (usually 5 to 7), the upper stem leaves often over-topping the terminal spike. Stem leaf sheaths are concave to U-shaped at the tip, translucent whitish to light brown. The ligule (membrane where the leaf joins the sheath) is as long as or shorter than wide. Leaves are hairless, green to yellowish-green, mostly erect, and have distinct cross partitions between the veins (septate-nodulose).

Bases are wrapped in a brown to pinkish sheath that is not much fibrous, if at all. Stems are mostly erect, spongy and somewhat thickened at the base, 3-sided in cross-section usually with blunt angles, slightly rough along the angles on the upper stem, and single or a few together. Stems can elongate up to about 3 feet at maturity. Plants often form large colonies from long, creeping rhizomes.

Fruit:

Fruit develops in late spring to mid-summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. Perigynia are ascending to spreading and tightly packed on the spike. Each pistillate spike contains 20 to 150 fruits.

Pistillate scales are lance to egg-shaped, white to brown tinged to purplish with a pale midvein, pointed or with a long taper to a pointed tip (rarely short-awned), narrower and mostly shorter than the perigynia. Perigynia are 4 to 8 mm long, 1.6 to 3 mm wide, greenish to straw-colored to brown at maturity, hairless, distinctly 9 to 15-veined, thin, much inflated, the body lance to egg-shaped, mostly broadest below the middle, tapering to a smooth beak 1.1 to 2.7 mm long that has 2 straight teeth at the tip. Achenes are 3-sided, brown at maturity, elliptic to urn-shaped with a persistent style.

Notes:

Carex utriculata is a common sedge of open, wet areas such as marshes, lake and pond margins, bogs and wet meadows in about 3/4 of Minnesota. It's often found growing in shallow water and forming large stands.

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 utriculata is in the Vesicariae section; some of its common traits are: clump forming or not, rhizomatous, hairless leaves, basal sheaths brown or red-purple, sheaths often splitting into fibers and forming a ladder shape, sheaths with cross partitions between veins (septate-nodulose), 2 to 10 spikes, terminal spike all-staminate, leaf-like bract subtending the lowest pistillate spike, perigynia mostly ascending to spreading, hairless, mostly egg to teardrop shaped, beaked and toothed, at least slightly inflated, achenes 3-sided in cross-section with a persistent style.

Carex utriculata is distinguished from all other Minnesota sedges by the combination of: colony-forming, brown to pinkish basal sheaths that are not much fibrous, 3-sided stems thickened and spongy at the base, stems slightly rough below the spike clusters, leaves flat or folded, widest leaves 4 to 12 mm, 1 to 5 staminate spikes, 2 to 5 cylindric short-stalked to stalkless pistillate spikes, perigynia inflated, 4 to 8 mm long, distinctly 9 to 15-veined and beaked, 3-sided achenes with a persistent style. The color of perigynia and scales is rather variable; we've seen perigynia early in the season that were nearly white while late in the season some were purple tinged. Likewise, scales range from pale brown to deep purple. Environmental factors may affect this.

C. utriculata was once considered a variety of Carex rostrata (Carex rostrata var. utriculata) so understandably they are very similar species. Both are colony-forming and may be found in some similar habitats, but C. rostrata tends to be a more slender plant with somewhat smaller perigynia, stems are round to weakly 3-sided and smooth just below the spikes, leaves are U-shaped in cross-section, more blue-green in color, the widest leaves are rarely more than 4 mm, and the upper leaf surface is covered in minute bumps (papillose), though strong magnification is required to see them. By comparison C. utriculata is more yellow-green, stems are more strongly 3-sided and often slightly rough along the angles especially just below the spikes, leaves are flat or folded (V-shaped), leaf surfaces are smooth, and widest leaves are usually at least 5 mm. See Michigan Flora for images of microscopic differences between C. utriculata and C. rostrata. Carex vesicaria also has similar spikes as these two but is densely clump-forming, not colony forming. C. utriculata rarely hybridizes with several other Carex species, including C. rostrata; hybrids are sterile and intermediate in characteristics.