lion's leaf

from the GNU version of the Collaborative International Dictionary of English.

• noun (Bot.) A South European plant of the genus Leontice (Leontice leontopetalum), the tuberous roots of which contain so much alkali that they are sometimes used as a substitute for soap.

from Wiktionary, Creative Commons Attribution/Share-Alike License.

• noun Leontice leontopetalum, a South European plant, whose tuberous roots contain so much alkali that they were sometimes used as a substitute for soap.