C. rupestris grows on dry to mesic heaths, meadows, gravelly ridges, rock outcrops and talus slopes.
Carex rupestris is an alpine species that is documented from 688-1492 m with an average plot elevation of 1167 m. It generally preferred steep sites with an average plot slope of 20 degrees. It strongly preferred south facing slopes.
Carex rupestris has a circumpolar worldwide distribution ranging across Eurasia, North America and Greenland. Carex rupestris occurs in suitable dry alpine habitat across Alaska and Canada south through the Rocky Mountain states to New Mexico as a high elevation species. In Alaska, C. rupestris occurs in most mountainous areas except for the Chugach and Kenai Peninsula, Alaska Peninsula and southeast panhandle. In Denali, C. rupestris occurs primarily on the north side of the Alaska Range in mountainous areas of the northeastern quadrant of the park. It is rarely seen south of the range, but occurs near Broad Pass and in the southwestern corner of the park near Shellabarger Pass.
Carex rupestris 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 gravity dispersed.
Carex rupestris flowers in early summer in Denali.
Carex rupestris is a small, tufted perennial sedge that occurs in dry tundra and rubble slopes, primarily north of the Alaska Range crest in Denali. This diminutive species has curling leaves and narrow solitary spikes, and is often associated with calcareous sites. Plants have an erect, slightly scabrous stem 8-15 cm tall arising from a brown or black rhizome. Leaves are about as long as the stem, flat or involute, scabrous and often curled and with scarious tips. Stems lack a subtendingbract. The inflorescence is a single erect spike, 6-20 mm long, with staminate (male) flowers at the tip, and a few pistillate flowers at the base. The pistillate scales are dark brown with a hyaline margin, wider than and about as long as the perigynia. The perigynia are three-angled, light brown with a short beak. The fruits are achenes with 3 stigmas. Plants could be confused with C scirpoidea, but that plant is dioecious—spikes are composed with entirely of staminate or pistillate flowers. C. obtusata is similar, but that species is taller, has a purplish rhizome and are shiny dark brown perigynia. No other alpine sedge in Denali has a single spike with distinctly curly leaves.