umbrella plantEnglishOxford New American Dictionaryumbrella plant /ˌəmˈbrelə plant, ˌəmˈbrɛlə plænt/ ▸ noun a tropical Old World sedge that has stiff green stems, each terminating in a whorl of arching green leaflike bracts. It is commonly grown as a houseplant. Cyperus alternifolius (or involucratus), family Cyperaceae.