Why Is the Pennyroyal Becoming Extinct?

McKittrick Pennyroyal

• The 1982 Amendment to the Endangered Species Act listed McKittrick pennyroyal, or Hedeoma apiculatum, as threatened due to its small population. At the time, botanists felt that the flower's small numbers reduced its reproductive potential, and that human impact impeded the pennyroyal's success. Later research demonstrated the flowering herb garnered a larger population density and range than previously known, and in 1993, the U.S. Fish and Wildlife Service took the McKittrick pennyroyal off the threatened species list.

False Pennyroyals

• Trichostema brachiatum, or "false pennyroyal," bears small pale-blue flowers each August. The erect herb grows in open, sunny spots across the eastern United States in USDA hardiness zones 4 to 7. In 1993, the government of the Commonwealth of Massachusetts declared false pennyroyal an endangered species due to habitat destruction. Another endangered false pennyroyal is Hedeoma hispidum, the "rough false pennyroyal." Kentucky, Ohio, and New York list Hedeoma hipsidum as a threatened species.

Flagstaff Pennyroyal

• Hedeoma diffusum, or "Flagstaff pennyroll," grows 7,500 feet high in the soil-filled cracks of boulders and limestone-pockets that line the mountainsides in the region surrounding Flagstaff, Arizona. NatureServe, an encylopedia of living species of North America, places the Flagstaff pennyroyal at moderate risk of extinction because the herb grows in only 60 known locations. The Flagstaff pennyroyal also suffers from competition with nonnative weeds, or when animals graze the plant excessively.

Todsen's Pennyroyal

• Hedeoma todsenii, or "Todsen's pennyroll," grows in 18 sites in the wooded foothills of the Sacramento mountains in New Mexico. The U.S. Fish and Wildlife Service listed Todsen's pennyroyal as an endangered species in 1981, due to soil erosion and wildfires and damage from grazing animals and mining activities. NatureServe rates the herb as imperiled, or at high risk of extinction. A 2001 Recovery Plan updated the list of threats to Todsen's pennyroyal to include low genetic diversity among a small number of populations, and a low reproductive rate due to inefficient dispersal patterns.