Carex tenuiflora is a tufted sedge with few-flowered green spikes that occurs in peatland bogs, pond margins and other wet areas in the boreal zone on both sides of the Alaska Range crest in Denali. Plants grow from slender rhizomes. Stems are slender, somewhat arching, 10-50 cm tall. The leaves are narrow, canaliculate or flat, grayish green. Inflorescence is comprised of 2-4 spikes, all closely clustered at the end of the stem. Spikelets are all bisexual, the pistillate (female) spikes produced above the male. The scales are transparent, papery and about the same size as the perigynia, with 3 green nerves. The perigynia are green, faintly veined, elliptic and beakless. The achenes are pale brown, flattened and shiny, with two stigmas. Carex tenuiflora looks very similar to the uncommon C. loliacea, but the spikes are more widely spaced in that species and the perigynia are strongly veined.
Carex tenuiflora flowers and fruits from May to August.
Carex tenuiflora is monoecious, but male and female organs are produced in separate flowers, in the same spike. Species in the genus Carex are wind pollinated, but usually also self-pollinate to some degree (Bertin 2007; Friedman and Barrett 2009). Seeds are wind and water dispersed.
Carex tenuifolia is a widespread incompletely circumpolar species that occurs widely in the Northern Hemisphere, but is absent from Greenland. In North America, this species occurs across Alaska and Canada, extending south to the upper Midwest and New England in the east and Washington State and Montana in the west. In Alaska, C. tenuiflora occurs scattered in boreal regions, with a few isolated stations on the Arctic slope. In Denali, this species is widespread in suitable wetland habitat, occurring on both sides of the Alaska Range.