A year ago today, we mistook this Lucrezia Borgia of the plant world for "a lovely intruder" in our garden. Now scientists have discovered the devious methods used by the weedy garlic mustard (Alliaria petiolata, AKA Alliaria officinalis) to invade and destroy our native hardwood forests. (Harvard Gazette photo)
"An invasive weed that has spread across much of the United States harms native maples, ashes, and other hardwood trees by releasing chemicals harmful to a soil fungus the trees depend on for growth and survival, scientists reported in the Public Library of Science," says The Harvard Gazette:
The tree-stifling alien, garlic mustard (Alliaria petiolata), first introduced into the United States in the 1860s, has since spread to Canada and 30 states in the East and Midwest, with recent sightings as far west as Oregon.
"While vanishing habitat caused by human activity is the number one threat to biodiversity [that's debatable], there is great concern over the impact of accidental and intentional dispersal of alien invasive species across the globe," says Kristina A. Stinson, a plant population biologist at the Harvard Forest, Harvard's ecology and conservation center in Petersham, Mass.
Like garlic mustard, Lucrezia Borgia was reputed to have used poison to dispatch her enemies. (Detail of Portrait of a woman by Bartolomeo Veneto, traditionally assumed to be Lucrezia Borgia according to Wikipedia, which gets the artist's name wrong)
"Stinson and her colleagues found that garlic mustard targets arbuscular mycorrhizal fungi (AMF), which form mutually beneficial relationships with many forest trees,"
These fungi have long filaments that penetrate the roots of plants, forming an intricate interwoven network that effectively extends the plant's root system. AMF depend on plants for energy and plants depend on the fungi for nutrients. When tree seedlings, which depend strongly on AMF, began to decline in the presence of garlic mustard, the researchers suspected that the invasive plant might thwart this symbiotic relationship [using] phytochemical poisons to disrupt native plants' mycorrhizal associations and stunt their growth.
Phytoterrorism in our own backyard.