Plants without conspicuous rhizomes. Culms 30-120 cm, 2.5-4 mm wide basally, 0.7-1 mm wide distally. Leaves: proximal sheaths loose, longitudinally green-and-white-striped and green-and-white-mottled on back, with prominent transverse veins, fronts hyaline, transversely rugose; ligules 3-7 mm, slightly longer than wide; widest leaf blades (4-)5-8 mm wide. Inflorescences with 5-10 spikes, 1.5-4 cm × 8-10 mm; proximal internodes usually not more than 10 mm, 0.7-1.5(-2) times as long as proximal spikes; proximal bracts to 2 cm; spikes with 6-20 ascending to spreading perigynia. Pistillate scales hyaline or pale brown with green midvein, ovate-circular, 1.5-2 × 1.1-1.5 mm, 1/2 length of perigynia, apex subobtuse to acute. Anthers 0.7-1.3 mm. Perigynia green, with narrow wing not more than 0.1 mm wide distally, weakly 4-7-veined abaxially, 3-4.5 × 1.5-2.5 mm, margins serrulate distally; beak 1-1.3 mm, apical teeth 0.2-0.5 mm. Achenes suborbiculate, 1.6-2 × 1.3-1.7 mm. 2n = 50.

Fruiting late spring-early summer. Dry to mesic deciduous and mixed forests and forest margins on neutral or basic soils; 20-300 m; N.B., Ont., Que.; Conn., Ill., Ind., Iowa, Maine, Mass., Mich., Minn., N.H., N.J., N.Y., Ohio, Pa., Vt., Wis.

Rich woods. In Indiana known only from two collections by Deam: beech-sugar maple woods a mile and a half west of New Waverly, Cass County; and low woods bordering Tippecanoe River north of DeLong, Fulton County. It is probably more frequent than the few collections would indicate since it resembles the ubiquitous C. sparganioides so closely that it is apt to be passed by as that species. The Tippecanoe County report by Smith is not supported by a specimen nor could any specimen be found to confirm Peattie's report from Lake County. Specimens of C. alopecoidea (§ Vulpinae) before fully mature, and particularly when from an open habitat, often closely simulate C. cephaloidea. These may be most readily distinguished by their acuminate to cuspidate or aristate pistillate scales which are more than half the length of the bodies of the perigynia and have a conspicuous green center. In C. cephaloidea the pistillate scales are obtuse or at most acute, half the length of the bodies of the perigynia or shorter, and are hyaline throughout (never becoming coppery-tinged at maturity as in C. alopecoidea) except for the faint green midrib.