PENNYROYAL, in botany, a herb formerly much used in medicine, the name being a corruption of the old herbalist's name " Pulioll-royall," Pulegium regium. It is a member of the mint genus, and has been known to botanists since the time of Linnaeus as Mentha pulegium. It is a perennial herb with a slender branched stem, square in section, up to a foot in length and rooting at the lower nodes, small opposite stalked oval leaves about half-inch long, and dense clusters of small reddish-purple flowers in the leaf axils, forming almost globular whorls. It grows in damp gravelly places, especially near pools, on heaths and commons. It has a strong smell somewhat like that of spearmint, due to a volatile oil which is readily obtained by distillation with water, and is known in pharmacy as Oleum pulegii. The specific name recalls its supposed property of driving away fleas (pulices). Like the other mints it has carminative and stimulant properties.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)