[508] Malone observes that there is no ground for supposing that rue was called “herb of grace” from its being used in exorcisms in churches on Sunday, a notion entertained by Jeremy Taylor, who says, referring to the Flagellum Dæmonum , “First, they (the Romish exorcisers) are to try the devil by holy water, incense, sulphur, rue, which from thence, as we suppose, came to be called ‘herb of grace.’”
— from Folk-lore of Shakespeare by T. F. (Thomas Firminger) Thiselton-Dyer