Cyperus grayoides is a species of sedge known as Illinois flatsedge and Mohlenbrock's umbrella sedge. It is endemic to the United States, where its distribution extends from Illinois through Missouri and Arkansas to Texas and Louisiana. This perennial herb grows from a network of tuberous rhizomes, producing clumps of triangular stems up to 35 to 48 centimeters tall. The gray-green leaves are up to 25 centimeters long. The inflorescence is a cluster of several rounded spikes containing many spikelets.