Migration
On the left, a picture of blooming garlic mustard. Seed pods are long and green and branch off of the main stem.
On the right, mature garlic mustard seed pods. Seed pods are brown and dry.
On the right, mature garlic mustard seed pods. Seed pods are brown and dry.
How It Spreads
Garlic mustard was originally introduced into North America by humans for culinary and medicinal purposes in 1860. Since then, it has taken over almost all of the undergrowth of the places it invades. It has survival adaptions that allow it to live in many environments, and adapt to new ones that it takes over.
It could spread so quickly because its seed pods dry out in the heat, and the seeds are carried about by the wind. Animals also help with the spread of the plant by dispersing them by kicking or stepping on the plant, which will release the seeds.
Since garlic mustard can either cross-pollinate or self-pollinate it is much easier for the seeds to germinate. When it self pollinates, it produces an exact copy of itself, which allows it to keep all of its survival adaptions. If that parent plant has the perfect genotype for the environment, self pollination will allow all of the other plants to have that same genotype, therefore increasing their lifespan and rate of growth.
Garlic mustard has had so much success spreading in its new environment because of the lack of predators in North America. Almost none of the insects that live in Europe and eat garlic mustard are present in North America. That allows it to out-compete other plants in its ecosystem without any struggle. It makes up the majority of undergrowth in many forests in the states it has taken over because it has grown in place of the other native plant species.
It could spread so quickly because its seed pods dry out in the heat, and the seeds are carried about by the wind. Animals also help with the spread of the plant by dispersing them by kicking or stepping on the plant, which will release the seeds.
Since garlic mustard can either cross-pollinate or self-pollinate it is much easier for the seeds to germinate. When it self pollinates, it produces an exact copy of itself, which allows it to keep all of its survival adaptions. If that parent plant has the perfect genotype for the environment, self pollination will allow all of the other plants to have that same genotype, therefore increasing their lifespan and rate of growth.
Garlic mustard has had so much success spreading in its new environment because of the lack of predators in North America. Almost none of the insects that live in Europe and eat garlic mustard are present in North America. That allows it to out-compete other plants in its ecosystem without any struggle. It makes up the majority of undergrowth in many forests in the states it has taken over because it has grown in place of the other native plant species.
Sources
Information: Wikipedia; http://en.wikipedia.org/wiki/alliaria_petiolata, National park service; http://www.nps.gov/plants/alien/pubs/midatlantic/alpe.htm
Images: Minnesota wild flowers; http://www.minnesotawildflowers.info/flower/garlic-mustard, Wild man Steve Brill; http://www.wildmanstevebrill.com/Plants.Folder/Garlic%20Mustard.html
Images: Minnesota wild flowers; http://www.minnesotawildflowers.info/flower/garlic-mustard, Wild man Steve Brill; http://www.wildmanstevebrill.com/Plants.Folder/Garlic%20Mustard.html