Parthenium hysterophorus (bitterweed, carrot grass, false ragweed, feverfew, parthenium weed, whitetop, ragweed parthenium, whitehead, barley flower, congress grass, amargosa)

summer annual

place of origin:
Mexico, Central and South America

urban habitat: commonly found in disturbed sites, waste areas, along roadsides.

ecological function: fast growing pioneer species; food for wildlife.

history: Parthenium hysterophorus is found throughout the eastern US and was introduced into Africa, Asia, Australia and Oceania through contaminated cereal and grass shipments from the US in the 1950’s. Outside of its native range it is widely considered an invasive presence. The plant has been used medicinally in its native range, as well as in India, for treatment of a wide variety of maladies, including headache, backache, arthritis, cold, coughs, diarrhea, fever, rheumatism, skin eruptions, malaria, and used as an insect repellent. It has recently been discovered to demonstrate anti-tumor activity in laboratory studies. Contact with the plant can cause dermatitis and respiratory problems in humans and other mammals due to the presence of the toxin parthenin. The plant has been found to be resistant to popular herbicides containing glyphosate.