Carex klamathensis is a rare species of sedge known by the common name Klamath sedge. It is known from 15 or fewer populations in southern Oregon and three populations in the Klamath Region of northern California. It was described to science only in 2007. Its habitat includes fens and other wet habitat, on serpentine soils. This sedge grows from a long rhizome bearing clumps of stems. The leaves are glaucous, 2-6 mm wide, with papillae between and sometimes over the veins. The inflorescence consists of 2-3(-5) spikelets. The terminal spikelet is usually staminate, occasionally androgynous, gynecandrous, or pistillate. Staminate terminal spikes are 1. 3-2. 7 cm long, 2-5 mm wide, with 40-190 flowers. Lateral spikelets are pistillate, (0. 6-)1. 5-2. 5 cm long, 4-7 mm wide, the uppermost usually 1. 5-6 cm or more below the terminal spike, but sometimes attached as close as 0. 3 cm below the terminal spike. Pistillate flower bracts are reddish brown, dark brown, or rarely gold, the midrib and surrounding area green, white, or light brown, the edges sometimes pale, 1. 9-2. 8 mm long excluding awn.