This is a widespread variable circumboreal species; 2n = 20-58 (FNA 23). It typically occurs on somewhat stagnant shores with much fine clay and rather low fertility, but with a pH ranging from 3 to 7 (Rothrock & Wagner 1975). The superficially similar tenuis (as well as its relatives) is generally less slender in its culms and rhizomes, and is more confined to acid sites, often with sand. E. acicularis (together with other species in section Scirpidium) has distinctive achenes with several distinct longitudinal ribs with very narrow horizontal cells between (FNA 23; W). Several uncertain records from Ky. are based on immature spikelets, but vegetative characters suggest acicularis. See also notes under E. microphylla, which may be confused.