bachelor's button

noun[usually plural]4

1. •
   Any one of a number of plants with daisy-like, button-shaped flowers of the genus Centaurea, especially the species Centaurea cyanus.

   • Jane picked up her hat from the bed. It was a pretty hat, with a wreath of bachelor’s buttons around it. — 1930
2. •
   feverfew, Tanacetum parthenium.
3. •
   The plant Ranunculus aconitifolius.
4. •
   A button which may be attached to clothing without resorting to needle and thread.