A species of very wet swamps and buttonbush marshes, barely ranging as far north as Michigan. Well-developed inflorescences are strongly nodding. Not collected in Michigan since 1891, and apparently extirpated in the state, but Dewey (1834) comments “Found abundantly by Dr. Folwell in a swamp near the river Raisin, in Michigan Territory.” The Washtenaw Co. specimen, from the Allmendinger herbarium, lacks any data but "Ann Arbor" and may be a duplicate of one of the other Michigan collections where the data has been lost.

Some robust specimens of C. sparganioides with the lower spikes compound may seem to run here, but may be distinguished by their larger (ca. 3–4.1 mm), thin, ovate, narrowly winged, bright to light green (turning yellow) perigynia; and usually by the absence of purplish dots on the ventral surface of the upper leaf sheaths. (In C. decomposita, the perigynia are smaller, biconvex-obovoid, and very dark green to brown at maturity; and the sheaths are dotted with purplish-brown). Furthermore, the anthers of C. sparganioides are often less than 1 mm long.