Plants densely cespitose. Culms 20-80 cm. Leaves: sheaths adaxially conspicuously green-veined nearly to collar, narrow hyaline band or sharp Y-shaped region at collar; summits U-shaped; distal ligules 2-4 mm; blades 3-5 per fertile culm, 14-25 cm × 1-3 mm. Inflorescences usually nodding, ± open, yellow-brown or reddish brown, 2.5-6 cm × 5-16 mm; proximal internode (2-)5-16 mm; 2d internode 5-17 mm; proximal bracts bristlelike. Spikes 3-9, distant, distinct, ellipsoid, 6-15 × 4-8 mm, base acute, apex obtuse; lateral spikes with staminate portion 2 mm or less at base. Pistillate scales reddish brown, often with green or pale midstripe, lanceolate, 3.5-4.9 mm, shorter and much narrower than perigynia, margin reddish brown, apex firm, acuminate or awned. Perigynia spreading, reddish brown, conspicuously 5-veined or more on each face, lance-ovate to weakly obovate, flat except over achene, 3.8-5.6 × 1.9-2.8 mm, 0.4-0.5 mm thick, base rounded, margin flat, including wing 0.4-0.7 mm wide; beak ascending, reddish brown at tip, flat, 1/2 length of body, ciliate-serrulate, abaxial suture with brown or reddish brown-hyaline margin, distance from beak tip to achene 2-3 mm. Achenes elliptic, 1.5-1.8 × 0.9-1.1 mm, 0.3-0.4 mm thick. 2n = 74.
Fruiting mid summer. Maritime rock ledges, brackish or freshwater marshes, moist coastal sands; 0 m; St. Pierre and Miquelon; N.B., Nfld. and Labr. (Nfld.), N.S., P.E.I., Que.; Conn., Del., Maine, Md., Mass., N.H., N.J., N.Y., N.C., R.I., Va.
Some authors have treated Carex hormathodes as a variety of C. straminea. Characteristics of the perignyium beak and spike base, as well as the distinctive habitat and range clearly differentiate the taxa (P. E. Rothrock et al. 1997).