What is "herb grace"

Herb \Herb\ ([~e]rb or h[~e]rb; 277), n. [OE. herbe, erbe, OF. herbe, erbe, F. herbe, L. herba; perh. akin to Gr. forbh` food, pasture, fe`rbein to feed.]

1. A plant whose stem does not become woody and permanent, but dies, at least down to the ground, after flowering.

   Note: Annual herbs live but one season; biennial herbs flower the second season, and then die; perennial herbs produce new stems year after year.

2. Grass; herbage.

   And flocks Grazing the tender herb.
   --Milton.

   Herb bennet. (Bot.) See Bennet.

   Herb Christopher (Bot.), an herb ( Act[ae]a spicata), whose root is used in nervous diseases; the baneberry. The name is occasionally given to other plants, as the royal fern, the wood betony, etc.

   Herb Gerard (Bot.), the goutweed; -- so called in honor of St. Gerard, who used to be invoked against the gout.
   --Dr. Prior.

   Herb grace, or Herb of grace. (Bot.) See Rue.

   Herb Margaret (Bot.), the daisy. See Marguerite.

   Herb Paris (Bot.), an Old World plant related to the trillium ( Paris quadrifolia), commonly reputed poisonous.

   Herb Robert (Bot.), a species of Geranium ( Geranium Robertianum.)