ipomoea purga

Ipomoeic \Ip`o*m[oe]"ic\ ([i^]p`[-o]*m[=e]"[i^]k), a. (Chem.)
   Pertaining to, or designating, an acid obtained by the
   oxidation of convolvulin (obtained from jalap, the tubers of
   {Ipom[oe]a purga}), and identical in most of its properties
   with sebacic acid.
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Jalap \Jal"ap\, n. [F., fr. Sp. jalapa; -- so called from
   Jalapa, a town in Mexico, whence it was first obtained.]
   (Med.)
   The tubers of the Mexican plant {Ipom[oe]a 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 {Ipom[oe]a} yield several inferior kinds of jalap,
   as the {Ipom[oe]a Orizabensis}, and {Ipom[oe]a tuberosa}.
   [1913 Webster]

   {False jalap}, the root of {Mirabilis Jalapa}, four-o'clock,
      or marvel of Peru.
      [1913 Webster]