Plants cespitose. Culms acutely angled, 30–50 cm, scabrous. Leaves: basal sheaths red-brown, ladder-fibrillose; sheaths of proximal leaves glabrous, fronts red-brown spotted, veinless; blades 2.5–4 mm wide. Inflorescences: proximal bract subequal to inflorescence, 1–3 mm wide. Spikes erect; proximal 3–4 spikes pistillate, 2.5–4 cm × 4 mm, base attenuate; terminal 1–2 spikes staminate. Pistillate scales red-brown, shorter than perigynia, apex obtuse, awnless. Perigynia erect, orange-brown at maturity, veinless, somewhat flattened, tightly enclosing and distended by the achenes, obovoid, 2.3–2.5 × 1.3–1.5 mm, dull, apex acute, glabrous; beak white with red-brown spots, triangular, often twisted, 0.5–0.8 mm, orifice oblique. Achenes not constricted, dull.

Fruiting May–Jun. Marshes, stream banks; of conservation concern; 0–400 m; Ariz.; Mexico.

One locality for Carex endlichii is known from the Chiricahua Mountains of southern Arizona; it may be present at additional sites within the flora area. The perigynium surface of the species is unique, becoming orange-brown at maturity due to the dense packing of crystalline epidermal cells. The small size of the perigynia that tightly enclose the achenes and the flattened, somewhat twisted beak suggest a relationship with C. interrupta and C. torta.