thumb|right|Chemical structure of [[scammonin|scammonin I, one of the primary chemical constituents of jalap]]
Jalap is a cathartic drug, largely obsolete in Western medicine, consisting of the tuberous roots of Ipomoea purga, a convolvulaceous plant growing on the eastern declivities of the Sierra Madre Oriental of Mexico at an elevation of above sea level, more especially about the neighbourhood of Chiconquiaco on the eastern slope of the Cofre de Perote in the state of Veracruz.
Ipomoea jalapa is yet another morning glory species from which jalap is obtained; it was first scientifically described (as Convolvulus jalapa) by Linnaeus. However, it is not of great commercial importance. As it also occurs in Veracruz, it was long confused with I. purga, even by such eminent botanists as David Don, Thomas Nuttall or C.J.W. Schiede. Consequently, the name I. jalapa is often seen as an invalid junior homonym referring to I. purga, in particular in sources older than 1989 (when the confusion was finally resolved). Throughout much of the 20th century, the I. jalapa of Linnaeus was called I. carrizalia.
See also
- Ipomoea