Pennyroyal is variety of mint that grows 4 to 12 inches (10 to 30 cm) tall, with narrow, bright green leaves up to 1 inch (2 1/2 cm) long.The stems will put out roots whenever they touch the soil.
It has the scent of peppermint.
Pennyroyal used to be a good deal in cooking, for teas, and for medicines. However, the latest studies show that it can have toxic effects on the liver and on women in particular, and so the recommendation is that it should not be consumed or taken internally in any way.
The Romans and Greeks used it. The Roman food writer Apicius calls for it in several of his recipes.