Cyperus is an enormous and ancient genus of sedges found throughout tropical and temperate regions worldwide, growing in the still or slow-moving water and saturated soils where most ornamental plants struggle. Heights range from a few inches to four feet depending on species, and the habit is typically upright and grass-like, with basal green leaves and triangular or rounded stems that carry small, greenish, wind-pollinated flowers in fall. Some species spread by seed, others by tubers, and a handful are aggressive enough to be considered invasive where conditions suit them.

The genus includes plants of genuine garden value for pond margins, rain gardens, and boggy spots where structure and movement are wanted. Butterflies visit the plants, and the upright, architectural habit provides winter interest even after the season has ended. The cardinal rule with Cyperus is to research the specific species before committing: the gap between a well-behaved ornamental and an unkillable weed can be a matter of a single species name.