wall-flower

a person who, because of shyness, unpopularity, or lack of a partner, remains at the side at a party or dance.

any person, organization, etc., that remains on or has been forced to the sidelines of any activity: The firm was a wallflower in this year's bidding for government contracts.

a European plant, Cheiranthus cheiri, of the mustard family, that, when growing wild on walls, cliffs, etc., has sweet-scented, usually yellow or orange flowers, but when cultivated has flowers varying in color from pale yellow to brown-red or purple.

any of several related plants of the genera Cheiranthus and Erysimum.