bladder campion

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A weedy perennial herb (Silene vulgaris) native to Eurasia, having white flowers with deeply notched petals and a balloonlike, inflated calyx.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun A perennial European herb, Silene vulgaris, having an inflated calyx

from WordNet 3.0 Copyright 2006 by Princeton University. All rights reserved.

• noun perennial of Arctic Europe having large white flowers with inflated calyx
• noun bluish-green herb having sticky stems and clusters of large evening-opening white flowers with much-inflated calyx; sometimes placed in genus Lychnis