An Indexed Bibliography. The Scientific Literature on Selected Herbs, and Aromatic and Medicinal Plants of the Temperate Zone. European pennyroyal is a low, prostrate, and spreading perennial herb, native to Europe and western Asia. Reaching a height of 0.3 meters, the plant has ovate to nearly orbicular leaves and lilac flowers.
American pennyroyal is a low-growing annual plant, native to the eastern part of the United States.
Reaching a height of 0.3 meters, the plant has multibranched pubescent stems, small, narrow, elliptic leaves, and light blue to purple flowers that appear in the summer months. American pennyroyal grows on dry, sandy soils and is commercially cultivated to only a very limited extent. The essential oil of pennyroyal is obtained by steam distillation from leaves and flowering tops. American pennyroyal has a similar essential oil. The essential oil is used as a fragrance in cosmetics.