Spikes:

A cluster 1 to 2½ inches long at the top of the stem, compound with 6 to 15 branches, the lower branches usually distinct with a few stalkless spikes each and the upper branches more obscure often with a single spike. Branches are mostly closely overlapping, though the lowest branch is occasionally farther separated. All spikes are alike with staminate (male) flowers at the tip and pistillate (female) flowers at the base (androgynous). At the base of each spike is a bristle-like bract, the lowest bract longest and usually shorter than the associated branch and does not over-top the terminal spike; bracts become shorter as they ascend the stem and are obscure in the uppermost spikes.

Leaves and stems:

Leaves are basal and alternate, mostly near the base, 3 to 6 mm wide, shorter than to about as long as the flowering stems. Stem leaf sheaths are straight across to concave at the tip, smooth (not wrinkled) on the front, tightly wrap the stem, firm and not easily torn, translucent with a thickened, white to yellowish band across the tip edge (may be more easily felt than seen). The ligule (membrane where the leaf joins the sheath) is longer than wide, pointed at the tip. Leaves are hairless, bright green to yellow-green, and V-shaped in cross-section when young.

The back of the sheath usually has distinct cross partitions between the veins (septate-nodulose). Bases are wrapped in a brown sheath that does not persist to the next season. Stems are erect to ascending, strongly 3-sided with narrow wings, stout but spongy and easily compressed, rough textured, elongating up to about 30 inches at maturity. Plants are clump-forming and not colony-forming. 

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. Pistillate spikes each contain 4 to 10 fruits that are ascending to spreading and crowded on the stalk.

Pistillate scales are lance-shaped, translucent whitish to brown with a green midrib, tapering to a pointed tip or the midrib extending to a short awn, and are about ¾ as long as the perigynia. Perigynia are 4 to 5 mm long, 1.2 to 2 mm wide, light brown to red-brown at maturity except paler at the base, obscurely veined on the back, more distinctly 7-veined on the front, hairless, not inflated but spongy at the base, flattened on the back side, narrowly triangular to somewhat fiddle-shaped in outline at maturity with a slight constriction between the achene and the spongy base, widest at the base, the base straight across or rounded but abruptly tapered to a short stalk-like structure (stipe), the tip with a long taper to a toothed beak to 2.5 mm long (1 to 2 times as long as the body) and is finely toothed along the edges. Achenes are 1.5 to 2 mm long and 1.3 mm wide, flattened lens-shaped, egg-shaped, and mature to brown.

Notes:

Carex laevivaginata is a rare sedge in Minnesota, where it reaches the northwestern edge of its range. According to the DNR, its preferred habitat is groundwater seeps in our southeast blufflands, which are very fragile habitats and rare in themselves. Any disruption in water flows, even from miles away, can negatively impact the vegetation. Due to this, C. laevivaginata was listed as a Threatened species in 1996. It is currently listed as Endangered in Wisconsin.

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 laevivaginata is in the Vulpinae section; some of its common traits are: clump forming, stems usually spongy, basal sheaths fibrous or not, sheath fronts cross-wrinkled (rugose) or not, leaves hairless and V-shaped in cross-section when young, spike clusters branched (compound) or not (simple) and often crowded, 4 to 20 stalkless spikes, terminal spike with staminate flowers at the tip (androgynous), lateral spikes androgynous or all pistillate, perigynia twice or more as long as wide, widest at/near the base, the base rounded with spongy tissue, tapered at the tip to a toothed beak, flattened lens-shaped achenes. Several of these traits are shared with the Phaestoglochin and Multiflorae sections; both have perigynia widest near the middle and usually less than twice as long as wide, firm stems, and the former usually has more than 15 spikes.

Carex laevivaginata is distinguished by its stems that are stout but easily compressed and strongly 3-sided with narrow wings; firm leaf sheaths that have a thickening at the tip (you may feel a bump when you run your finger over it), straight across to convex at the tip; cluster usually branched at least at the base, spikes/branches mostly closely overlapping, androgynous spikes; perigynia 4 to 5 mm long, narrowly triangular, straight across the spongy base and a long taper to a toothed beak; pistillate scales that are shorter than the perigynia and tapered to a pointed tip, sometimes awned. Most similar is the very common Carex stipata, which has fragile sheaths cross-wrinkled across the front.