Spikes:

Usually a single spike up to 1½ inches long at the top of the stem, occasionally with 1 to 3 small spikes at the base. Spikes typically have pistillate (female) flowers at the tip and staminate (male) flowers below (gynecandrous), but may also be all-staminate or all-pistillate. On a mixed spike, the proportion of staminate to pistillate flowers is highly variable, from just a few staminate flowers to nearly all staminate. A bract at the base of the spike is usually absent.

Leaves and stems:

2 to 6 leaves are alternately attached to the stem near the base, each 2 to 24 inches long, the widest leaves up to 1.5 mm wide, about as wide as and usually shorter than the flowering stems. Leaves are hairless, stiff, and rolled in along the edges (involute). The sheath front is membranous, translucent and concave at the tip. The ligule (membrane where the leaf meets the sheath) is rounded and about as long as or slightly longer than wide.

Bases are wrapped in a brown sheath that is not fibrous. Stems are mostly erect, 3-sided, very slender, elongating up to 32 inches at maturity and remain mostly longer than the leaves. Plants typically form dense clumps from short rhizomes.

Fruit:

Fruit develops in late spring to early-summer, the spike forming a cluster of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. A spike contains up to 27 fruits, mostly crowded and widely spreading.

Pistillate scales are egg-shaped with a blunt to pointed tip, turning brown with whitish edging on the tip half, and are slightly shorter than the perigynia. Perigynia are 2.6 to 4.7 mm long, 1.2 to 2.3 mm wide, 15-veined on the front and faintly veined on the back (more visible when mature and dry), brown to chestnut colored when mature, lance to egg-shaped, rounded and spongy at the base, tapering to a short beak with 2 small teeth at the tip and fine serrations along the edges. Achenes are 1.4 to 2.2 mm long, 1.2 to 1.7 mm wide, lens-shaped.

Notes:

Carex exilis is a sedge of open peatlands and patterned fens, often locally abundant in its preferred habitat, and reaches the western edge of its range in Minnesota. According to the DNR, these habitats are rare in themselves, and vulnerable to hydrology changes from human activities as well as climate change, which puts their specialized plant communities at risk, including Carex exilis. It was subsequently listed as a Special Concern species in 1984.

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 exilis is a member of the Stellulatae section; some of the section's common traits are: clump forming, basal sheaths not fibrous, leaves V-shaped in cross-section when young, usually 2 to 10 spikes per stem, terminal spike staminate or pistillate or with pistillate flowers at the tip (gynecandrous), pistillate scales blunt to pointed at the tip, perigynia widely spreading, hairless, veined at least on one side, spongy at the base, 2 short teeth on the beak, achenes lens-shaped.

Carex exilis is distinguished from all other Carex species by its open fen or peatland habitat, (usually) single spike most of which have at least some pistillate flowers at the tip though some spikes may be all-staminate, and widely spreading perigynia that have finely serrated edges on the beak. The only other sedge in Minnesota that is very similar in form is Carex gynocrates, which also has a single spike with widely spreading perigynia, but it is a much smaller plant (under 12 inches), not clump-forming, is usually found in shady, mossy bogs and conifer swamps, has androgynous spikes (staminate flowers at the tip) rather than gynecandrous, and usually has no serrations on the perigynia beak.