The medieval vervain was identified with the “holy herb” known to the Greeks and Romans. Despite its unprepossessing appearance, common vervain is one of the great magico-medical plants of the Western tradition.
Many odde olde wives tales are written of Vervaine tending to witchcraft and sorcerie, which you may read elsewhere, for I am not willing to trouble your eares with supporting such trifles as honest eares abhorre to heare.
???John Gerard, The Herbal or Generall Historie of Plants, 1597