wallflower

(noun) any of numerous plants of the genus Erysimum having fragrant yellow or orange or brownish flowers.

(noun) perennial of southern Europe having clusters of fragrant flowers of all colors especially yellow and orange; often naturalized on old walls or cliffs; sometimes placed in genus Erysimum. Synonyms: Cheiranthus cheiri, Erysimum cheiri.

(noun) remains on sidelines at social event.