bulrush (n.)

"plant growing in marshy ground," having leaves that grow as stiff pithy or hollow stalks, Middle English rishe, resh, rosh, rush, etc., from Old English resc (Kentish), risc, rysc, from Proto-Germanic *rusk- (source also of Middle Low German rusch, Middle High German rusch, German Rausch, West Frisian risk, Dutch rusch), perhaps from PIE *rezg- "to plait, weave, wind" (source also of Latin restis "cord, rope"). Old French rusche probably is from a Germanic source.

The remarkable variations in the vowel of this word make its precise history far from clear. [OED]

The stalks were cut and used for various purposes, including making torches and finger rings; they also were strewn on floors as covering or when visitors arrived; it was attested a type of something weak or of no value by early 14c.