wallflower \wall"flow`er\, n.
   1. bot. a perennial, cruciferous plant cheiranthus
      cheiri, with sweet-scented flowers varying in color from
      yellow to orange and deep red. in europe it very common on
      old walls.
      1913 webster

   note: the name is sometimes extended to other species of
         cheiranthus and of the related genus erysimum,
         especially the american western wallflower erysimum
         asperum, a biennial herb with orange-yellow flowers.
         1913 webster

   2. a lady at a ball, who, either from choice, or because not
      asked to dance, remains a spectator. colloq.
      1913 webster

   3. bot. in australia, the desert poison bush gastrolobium
      grandiflorum; -- called also native wallflower.
      webster 1913 suppl.
see also:
cheiranthus cheiri cheiranthus erysimum western wallflower erysimum asperum gastrolobium grandiflorum 
native wallflower