Definition of "burstwort"

For some ordinary broths made of Eringos or Sea-Holme, and Burstwort, which twice or thrice I have swallowed downe at the request of some Ladies, who, more kindely then my disease is unkind, offred me the moity of theirs, have equally seemed unto me as easie to take as unprofitable in operation.

1603, Michel de Montaigne, translated by John Florio, Essays, III.13