Three square is an emergent plant with long, thin rhizomes. It is a good soil stabilizer because of its rhizomatous habit. The stems are strongly triangular, hence the common name. Waterfowl eat the seeds and use stands of plants for nesting cover. Muskrats eat rootstock and young shoots, and use the plant in building materials. Three square grows in fens, marshes, and lake shores in up to 6 inches of standing water.