Erysimum, genus Erysimum, also called Gillyflower. Bath and Body Works sells scented products with the scent of Wallflower. The term is also used to describe a person, usually a girl, who is pretty but never does anything but look pretty. She just sort of decorates the room and doesn't interact with others much. A scant is someone who isn't seen much. (it also means approximate measure in cooking)
Maybe a "Wallflower scant" is someone who isn't seen much, and when they are seen, just hang around the sidelines without a date.
Where have you seen this term?