cotton rush vs sedge

cotton rush and sedge both are nouns.

Word	Noun	Adjective	Verb	Adverb
cotton rush	Yes	No	No	No
sedge	Yes	No	No	No

As nouns, sedge is a hypernym of cotton rush; that is, sedge is a word with a broader meaning than cotton rush:

cotton rush: any sedge of the genus Eriophorum; north temperate bog plants with tufted spikes
sedge: grasslike or rushlike plant growing in wet places having solid stems, narrow grasslike leaves and spikelets of inconspicuous flowers

cotton rush (noun)	sedge (noun)
any sedge of the genus Eriophorum; north temperate bog plants with tufted spikes	grasslike or rushlike plant growing in wet places having solid stems, narrow grasslike leaves and spikelets of inconspicuous flowers