The tubers of the Mexican plant Ipomœa purga (or Exogonium purga) of the family Convolvulaceae, a climber much like the morning-glory. The abstract, extract, and powder, prepared from the tubers, are well known purgative (cathartic) medicines, and are also called jalap. Other species of Ipomœa yield several inferior kinds of jalap, as the Ipomœa Orizabensis, and Ipomœa tuberosa.  [1913 Webster]