Nutlet
nutlet: a small nut, thick-walled achene, or stone of a drupe; one-seeded portion of the fruit of some members of the Boraginaceae, Lamiaceae, or Verbenaceae
You would probably not be surprised to hear that a nutlet is a small nut, but it also describes the part of the fruit of certain members of the borage family, the mint or sage family or the verbena or vervain family.