Culms to 75 cm × 2 mm, scabrous. Leaves: sheath fronts indistinctly spotted pale brown or red, apex convex, membranous, rugose; ligule rounded, to 3 mm, free limb to 0.2 mm; blades 60 cm × 5 mm, shorter than flowering stem. Inflorescences spicate, 4–7 cm × 15 mm, with 10–15 branches, proximal usually distinct; proximal internodes to 1.5 cm; bracts setaceous, proximal 1–3 conspicuous, distal bracts scalelike. Scales hyaline, red-brown with narrow colorless margins, awn to 1.5 mm. Perigynia golden brown, 3-veined abaxially, body broadly elliptic to ovate, 2.2–3 × 1.5–2.2 mm, base rounded; beak 0.5–1.2 mm, 1/3 length of body. Achenes red-brown, circular, 1.2–1.5 × 1–1.2 mm, glossy.
Phenology: Fruiting Jul–Aug.
Habitat: Dry to moist, often calcareous soils in open habitats, mesic to wet meadows
Elevation: 0–1500 m
Ont., Que., Ark., Conn., Del., D.C., Ill., Ind., Iowa, Kans., Ky., La., Maine, Md., Mass., Mich., Minn., Miss., Mo., Nebr., N.H., N.J., N.Y., N.C., Ohio, Okla., Pa., R.I., S.C., Tenn., Vt., Va., W.Va., Wis.
Carex annectens is similar in appearance to C. vulpinoidea, but can readily be distinguished by the flowering stems longer than the leaves and the orange-yellow perigynia that are usually ovate to suborbicular and short-beaked. Furthermore, that species is ecologically distinct and grows in open, dry to moist soils; C. vulpinoidea prefers wetter soils. It may be closely related to C. triangularis, which differs in having wider perigynia with red crystalline inclusions. Some authors recognize two taxa within the species (C. annectens var. annectans and var. xanthocarpa), distinguished by differences in perigynium color, inflorescence compactness, and pistillate scale awn length. All those characters appear to vary independently and within the same plant. Further detailed study may clarify patterns of biological variation within the taxon.