Cyperus erythrorhizos Muhl.
Habitat: Alluvial or damp sandy soil, streambanks, shorelines, and wet areas. Though often on sandy substrate, Cyperus erythrorhizos is occasionally on mucky or peaty substrate.
Range: Southern New England, New York, Ontario, and North Dakota, south to Arkansas, Texas, and Arizona.
Aids to Identification: Members of this genus can be difficult to identify without careful examination of microscopic features and an overall knowledge of the group. Cyperus species are identified by their 2-ranked scales of spikes, triangular stems, terminal inflorescences, and styles deciduous from the achene. Cyperus erythrorhizos is a stout annual with red roots.
Phenology: Flowers August to October.
Synonyms: Cyperus halei Torr. ex Britt.
Known Distribution in Maine: This rare plant has been documented from a total of 1 town in the following county(ies): York. Cyperus erythrorhizos has been recently documented from three of the islands in Isle of Shoals.