Flower:

Separate staminate (male) and pistillate (female) spikes, with a single staminate spike up to about 1 inch long at the top of the stem. Below the staminate spike are 2 to 4 few-flowered, all-pistillate spikes, usually widely separated, though the uppermost 1 or 2 pistillate spikes may crowd the staminate spike. Lower pistillate spikes are longer stalked than upper spikes, the stalks smooth and mostly erect. Pistillate spikes each have a leaf-like bract at the base of the stalk that loosely sheaths the stem, the bracts usually greatly over-topping the terminal spike.

Leaves and stems:

Leaves are basal and alternate, the widest 2 to 4.5 mm wide, mostly floppy, shorter or longer than the flowering stem. Stem leaf sheaths loosely wrap the stem, are whitish and hairless; both bract sheaths and leaf sheaths are convex at the tip and are elongated 1 mm or more above the base of the blade. The ligule (membrane where the leaf joins the sheath) is about as long as wide. Leaves are hairless, M-shaped in cross-section when young.

Bases are wrapped in a reddish-purple sheath that is not fibrous. Stems are slender, 3-sided, hairless, smooth to slightly rough, erect to spreading, and may elongate up to 20 inches at maturity. Not all plants produce flowering stems. Plants form loose to dense clumps.

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 have 2 to 8 fruits, the perigynia ascending to erect and loosely overlapping on opposite sides of the stalk.

Pistillate scales are lance-ellliptic, whitish with a green midrib that extends to a rough-textured awn .7 to 4.1 mm long, the scale body half or more as long as the perigynia, with the awn often longer than the perigynia especially on the lower part of a spike. Perigynia are green to yellowish-green, 3.5 to 4.7 mm long, 1.6 to 1.9 mm wide, hairless, not inflated, 51 to 67 impressed veins, weakly 3-sided in cross-section, elliptic to somewhat urn-shaped and widest above the middle, gradually tapering at the base, more abruptly tapered at the tip to a straight, toothless beak .3 to 1.2 mm long. Achenes are 2 to 3.4 mm long, weakly 3-sided in cross-section, widest above the middle, tapering at the base and maturing to brown.

Notes:

Carex oligocarpa is an occasional sedge of deciduous woods, wooded bluffs and slopes, mostly along the Minnesota River valley and in the maple-basswood forests of our southeast counties. It reaches the northern edge of its range in Minnesota.

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 oligocarpa is in the Griseae section; some of its common traits are: clump forming or not, short to long rhizomatous, basal sheaths not fibrous, leaves M-shaped in cross-section when young, the leaf underside with 2 lateral veins more prominent than the midvein, widest leaves 6 mm or less, 3 to 6 spikes, terminal spike all staminate, lateral spikes mostly all pistillate, sometimes with a few staminate flowers at the tip (androgynous), lateral spikes subtended by a long-sheathing leaf-like bract, pistillate scales with a rough-textured awn, perigynia oval-elliptic and hairless with impressed veins (both fresh and dry), achenes 3-sided with 3 stigmas, usually growing in woodlands or open habitats.

Carex oligocarpa is distinguished from other Carex species by the combination of: clump forming, red-purple at the base, sheaths mostly convex at the tip and extended above the base of the leaf, all-staminate terminal spike, 2 to 4 pistillate spikes with 2 to 7 perigynia per spike, pistillate scales with a rough-textured awn often longer than the perigynia, perigynia with up to 59 impressed veins, the short beak straight and toothless.

Carex oligocarpa most closely resembles Carex hitchcockiana, which has larger perigynia, hairy sheaths, and is brown at the base. Perigynia with very short beaks resemble Carex grisea, which is essentially beakless, the uppermost pistillate spike almost always crowds the staminate spike, may have a few staminate flowers at the tip of pistillate spikes (androgynous), widest leaves are up to 8.2 mm, and basal sheaths are often brown or less strongly red-purple.