A spicy invader that might also make a spicy addition to your next salad.
Alliaria petiolata, otherwise known as garlic mustard, is an invader from Europe that has established populations in much of the United States. The plant can grow annually, biennially, or perennially in its native range but is typically an obligate biennial in the US, meaning it completes its lifecycle over two years. Seedlings germinate in the 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 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.
Native plants suffer the brunt of garlic mustard invasions through loss of soil nutrients, light, moisture, and space resulting from direct competition. In addition, garlic mustard roots 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 plant family Brassicaceae produce secondary compounds called glucosinolates which are distasteful to herbivores and toxic at high levels (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 locally eradicated through diligent management. Chemical removal of rosettes in their first year is possible, but nontarget impacts on native flora is a concern with this approach. On the other hand, mechanical removal prior to seed production and release can limit recruitment of future generations with minimal impact on native vegetation, but requires consistent effort. An added bonus of physical removal is the addition of a new and interesting ingredient to the dinner table.
(Garlic Mustard Species Profile originally published May 16th, 2011 by Sheina Sim)