Spikes:

Separate staminate (male) and pistillate (female) spikes, with a single staminate spike up to nearly 1 inch long at the top of the stem, which occasionally has a few pistillate flowers at the very tip (gynecandrous) or near the middle. Below the staminate spike are 2 to 5 all-pistillate spikes, the lowest spike may be widely separated from the spike above it and is typically stalked; the uppermost spikes are stalkless or nearly so and usually more crowded near the tip. At the base of each pistillate spike is a leaf-like bract that is up to 7 inches long, far over-topping the terminal spike. Pistillate spikes are stout, round to elliptic in outline, 1/3 to nearly 1 inch long, erect to ascending and pale green at flowering time with white, thread-like styles, the staminate flowers with creamy yellow stamens.

Leaves and stems:

Leaves are basal and alternate, mostly near the base, 1.6 to 4.7(6) mm wide, mostly shorter than the flowering stems. Stem leaf sheaths are membranous on the front side and U-shaped at the tip. The ligule (membrane where the leaf joins the sheath) on uppermost leaves may be straight or convex and more triangular below. Leaves are hairless though slightly rough along the edges.

Bases are wrapped in a light tan to green sheath that is not fibrous. Stems are slender, 3-sided, mostly erect and mostly smooth. Stems elongate up to 30 inches at maturity and are usually longer than the leaves. Not all plants produce flowering stems. Plants form loose to dense clumps from short rhizomes.

Fruit:

Fruit develops in late spring through mid-summer, the pistillate spikes forming clusters of seeds (achenes), each wrapped in a casing (perigynium), subtended by a scale. The empty staminate scales persist after fruit has dropped off. Pistillate spikes each contain up to 35 fruits that are tightly crowded on the stalk, widely spreading or those towards the base of the spike angled down (reflexed).

Pistillate scales are lance-oblong with a pointed tip, tinged reddish-brown with a green midrib, and shorter than the perigynia but mostly visible. Perigynia are 4 to 6.3 mm long, 1 to 1.9 mm wide, hairless, the body turning yellow at maturity, inflated and loosely wrapping the achene, 8 to 20 nerved (best seen when dry), somewhat irregular in shape but widest above the middle, tapering to a beak half or more as long as the body, the beak strongly angled, with 2 teeth at the tip and rough textured (scabrous) along the edges (strong magnification required to see the bumps). Achenes are 1.3 to 1.7 mm long, up to 1.2 mm wide, 3-sided in cross-section, and mature to dark brown.

Notes:

Carex flava is uncommon in Minnesota, found mostly along streams and rivers that drain into Lake Superior, and seepy areas in deciduous and mixed forests of northeastern Minnesota. According to the DNR, its specific habitat requirements are complex and may not be well understood and was the basis of listing it as a Special Concern species.

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 flava is in the Ceratocystis section; some of its common traits are: typically clump forming, leaves hairless, leaves V-shaped in cross-section when young, spikes short and stout, terminal spike either all staminate or with a few perigynia, perigynia tightly crowded on the spike, spreading to reflexed, round in cross-section, beaked, the beak usually toothed, 3-sided achenes.

Carex flava is very similar in appearance to two other Minnesota sedges: Carex cryptolepis and Carex viridula. C. flava is distinguished by perigynia up to 6.3 mm long, perigynia at the base of a spike reflexed, scabrous beaks that are strongly angled, and pistillate scales tinged dark reddish brown. By contrast, C. cryptolepis pistillate scales are about the same color as the perigynia and inconspicuous, its perigynia smaller (to 4.5 mm) with smooth beaks. C. viridula perigynia are also much shorter, mostly spreading, not reflexed, and beaks are shorter and mostly straight or only slightly angled.