This native sedge is 2 to 3 feet tall with long, thin leaves extending from the base of the stem and arching outward and downward towards their tip. It has coarse fibrous roots and short rhizomes.

The stem ends in a group of 3-8 oval spikelets. The inconspicuous top spikelet is thin and contains only male (staminate) flowers. These wither away soon after the pollen is released. All the other spikelets contain only female (pistilate) flowers, each flower having a long style that divides into three stigmas. The close packing of the flowers gives the short, fat female spikelets a bristly appearance. Frank's sedge blooms in early summer (photographed in May here) and is wind pollinated.

Frank's sedge is unusual in having a separate spikelet for male flowers, as most other Carex species have the male flowers on the same spikelet as the female flowers, but below them.

The seeds are eaten by birds, while caterpillars and grasshoppers eat the leaves.