Lettuce

=From the Oxford Companion to Food = This ancient lettuce "is also called 'prickly' or 'wood' lettuce".

The original reason for cultivating lettuce was probably medicinal. Wild lettuce and, to a lesser extent, its cultivated descendant contain a latex with a mildly soporific effect. This resembles and smells like the latex of the opium poppy, but the plants are not related

In the early Roman period lettuce was eaten at the end of a dinner to calm the diner and induce sleep. Later it was eaten at the beginning to stimulate appetite. This change would have coincided with the development of improved varieties which, selected for lack of bitterness, would have contained less of the narcotic substances. All these were still loose, headless types.

APICIUS also gives a recipe for a puree of lettuce and onions and Columella described how lettuce was pickled in vinegar and brine.