Species profile: Garlic mustard

A relative of a previously profiled invader (field mustard), garlic mustard is a tasty but unwanted newcomer to the eastern United States.  I found a nice healthy patch on my bike commute to work and have slowly made a dent to this year’s flowering individuals.

Species description

 

Garlic mustard patch I've been collecting. The leaf litter is covering up the rosettes that germinated this spring, but I'll get them next year! Photo credit: S. Sim

Alliaria petiolata, otherwise known as garlic mustard, is an invader from Europe that has established populations in much of the eastern United States and many states westward.  They can grow annually, perennially, or biennially in their native range but are typically obligate biennials in the US, meaning they complete their lifecycles in two years .  Seedlings germinate in the wet spring, and remain as rosettes over the winter until the following spring when they bolt and flower.  Like other members of the family Brassicaceae, garlic mustard flowers are radially symmetrical and comprised of four petals.  Once pollinated either through self or cross fertilization, its carpels form fruits called siliques which dehisce at the end of the growing season to release its seeds.  This is important as they can only propagate by seed which can travel several meters away from their parent.  Seeds can also spread longer distances  by hitchhiking on passing animals and people.

Garlic mustard flowers and immature siliques with my thumb for scale. Photo credit: S. Sim
Map of garlic mustard distribution in the US and Canada. Green indicates presence. Image credit: USDA Plants

Harvesting techniques

My technique for harvesting was to hold the main axial stalk firmly and close to the ground, wiggle, and pulling straight up.

Victorious harvesting! Flowering adults are easy to collect just by pulling straight up. Photo credit: S. Sim

Garlic mustard does not have a vast network of roots, so plants pull right up with minimal collateral damage.  Since they do not propagate vegetatively, you don’t have to worry about leaving bits of root around like you would with Phragmites.

Ecological impacts and management

Native plants suffer the brunt of garlic mustard invasions because of their susceptibility to lose soil nutrients, light, moisture, and space from direct competition.  In addition, garlic mustard roots also release chemicals that harm neighboring plants and mycorrhizal fungi which results in the inability of the roots of neighbors to take up water and nutrients.  Related to the threat to native flora is the subsequent threat to native fauna which rely on native plants for food, pollen, and nectar.

Further bolstering the fitness of garlic mustard in the new world is its release from co-evolved enemies.  Members of the Brassicaceae family produce secondary compounds called glucosinolates which are distasteful to herbivores and toxic at high levels (relative to body size), but tasty to people.  Herbivores in the US have not adapted or evolved to consume garlic mustard which increases survivorship of garlic mustard to reproduction.

Garlic mustard can be eradicated through tough and diligent removal efforts.  Chemical removal of rosettes in their first year is possible, but the presence of native flora must also be considered.  Repeated mechanical removal prior to seed production and release is necessary to stop the entrenchment of the next generation, and harvest will bring a new and interesting ingredient to the dinner table.

UPDATE: We also encourage you to check out http://garlicmustard.org/ to see how you can contribute to valuable scientific research while you harvest your next meal!

Sheina

A self-proclaimed modern day nomad, I was born in the Philippines, grew up in southern California—lived all over really—and now I do research as a graduate student in Indiana and the Pacific Northwest. Professionally speaking, my current area of focus is speciation and ecological genetics and genomics, and a common theme in my various projects over the years is evolution in agricultural systems. As a recipient of a GLOBES—an interdisciplinary program funded by the National Science Foundation (NSF) through the Integrative Graduate Education, Research, and Traineeship grant (IGERT) —fellowship, I have received training which has better enabled me to view and ponder topics without my science hat on. I take great joy in eating, cooking, and experiencing nature through various activities. I love to travel and anticipate many local and international invasivore field trips! Though my research interests do not directly involve the study of invasive species, I have had my fair share of negative encounters with environmentally noxious organisms in the midst of doing field research. I carry around a machete with which to combat my gnarly “Himalayan” foes, and my machete and I have raised more than a few eyebrows. Apart from my personal vendetta against these deliciously juicy pests, I feel that there are great advantages to linking our awareness of the natural world to our culture, and Invasivore is an avenue to do just that. I feel that an increase in general knowledge of invasive species will be of great benefit to the field of invasive species and conservation biology. Knowledge and awareness will lead to action, and action will lead to results!

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