Spikes:

Separate staminate (male) and pistillate (female) spikes, with 1 to 5 staminate spikes up to 4 inches long clustered at the tip of the stem. Below the staminate spikes are 2 to 5 erect to ascending, cylindric pistillate spikes, each 2 to 5 inches long, well separated from each other, the upper stalkless and the lower on short, erect stalks. Pistillate spikes sometimes have a few staminate flowers at the tip (androgynous) or near the tip (gynecandrogynous). At the base of each pistillate spike is a leaf-like bract that often over-tops the terminal spikes.

Leaves and stems:

Leaves are basal and alternate, 4 to 10 mm wide, the upper stem leaves often over-topping the terminal spike, usually sparsely covered in long hairs on the underside, especially near the base. Stem leaf sheaths are concave to U-shaped at the tip, the front typically reddish to brown, splitting into fibers with age, and densely short-hairy on both front and back surfaces, sometimes just near the tip, rarely hairless. The ligule (membrane where the leaf joins the sheath) is an inverted V-shape, longer than wide, often much longer.

Bases are wrapped in a sheath that is reddish to brown and fibrous, the fibers connected and forming a ladder pattern (ladder-fibrillose). Stems are hollow and spongy at the base, mostly erect, 3-sided in cross-section, and smooth but may rough on the upper stem. Not all plants produce flowering stems; vegetative stems are mostly hollow and taller than flowering stems. Plants are loosely clump forming and often form large colonies from long 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 mostly ascending and overlapping on the spike, may be loosely arranged at the base of the spike and more crowded above. Each pistillate spike contains up to 100 fruits.

Pistillate scales are lance to narrowly egg-shaped, reddish to brown with white edging and a green midrib, pointed at the tip or the midrib extending to a rough-textured awn, the scale body about half as long as the perigynia but with the awn may be as long as the perigynia. Perigynia are 6 to 10 mm long, 1.8 to 3.8 mm wide, green to yellowish at maturity, hairless, 12 to 21-veined, inflated but firm, the body narrowly teardrop-shaped and round in cross-section, with a long taper to a short, straight beak with 2 widely spreading teeth 1.2 to 3 mm long at the tip. Achenes are round to weakly 3-sided in cross-section, 2 to 3 mm long, maturing to yellow-brown, with a long, straight, persistent style.

Notes:

Carex atherodes is a common sedge of open wetlands, ditches, swales, shores and riverbanks, sometimes forming large colonies. It can tolerate some drying but is more often found in standing water, as deep as 30 inches.

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 atherodes is in the Carex section; some of its common traits are: clump forming, long-rhizomatous, basal sheaths fibrous and red to brown, leaves and/or sheaths sometimes hairy, leaves M-shaped to flat in cross-section, lower leaves with cross partitions between veins (septate-nodulose), 4 to 10 spikes, terminal spike all-staminate, 1 to 5 staminate spikes, lower 2 to 5 spikes pistillate, pistillate spikes erect to ascending, cylindrical, all-pistillate or with a few staminate flowers at the tip (androgynous), leaf-like bract subtending pistillate spikes, perigynia ascending, hairy or not, 12 to 26 veined, inflated, mostly teardrop-shaped with a long taper to a toothed beak, achenes 3-sided in cross-section with a long, persistent style. Members of the Carex section may resemble some species in the Paludosae or Vesicariae sections.

Carex atherodes is distinguished from all other Minnesota sedges by the combination of: stems hollow and spongy at the base, sheaths fibrous, especially basal sheaths, sheaths hairy, especially stem sheaths, leaves sparsely hairy on the underside especially near the base, ligule much longer than wide, hairless perigynia with a long taper to a beak and long, widely spreading teeth. When growing in deeper water the sheaths may be nearly hairless or hairy only at the tip of the sheath, in which case it more closely resembles Carex laeviconica, which is completely hairless, has shorter teeth on the perigynia beak that are mostly straight, not much spreading, the vegetative stems are solid, not hollow, and the ligule is rounded at the tip and about as long as wide. The general shape of the perigynia is also similar to Carex lacustris, which has very short teeth on the beak that are not spreading. Of note is that several references state Carex atherodes is clump-forming, but our observation is that it is weakly so at best with just 1 or a few stems and few leaves.