Grasslike or rushlike plant growing in wet places having solid stems, narrow grasslike leaves and spikelets of inconspicuous flowers WordNet 3.0 & Open English WordNet

Any plant of the genus Carex, the true sedges, perennial, endogenous herbs, often growing in dense tufts in marshy places. They have triangular jointless stems, a spiked inflorescence, and long grasslike leaves which are usually rough on the margins and midrib. There are several hundred species. Wiktionary

Any plant of the genus Carex. Wiktionary (translation)