Garlic mustard, also called Jack-by-the-hedge and sauce-alone, is a biennial plant in the mustard family and a seriously invasive alien plant. Left to itself, it can completely take over an area, crowding out all native plants. It grows along shaded roadsides, woody paths, and other shady areas.
I noticed this growing in our backyard, along the wooded areas, years ago now but in the last couple of years it's exploded and taken over! Not only do I see it in the neighbors yard but along the roadways and parking lots too. I also find plants attempting to grow in our flower beds and raspberry beds - it's everywhere.
I guess it shouldn't be a surprise since the maximum production on one plant with 12 stems is estimated at 7,900 seeds, yikes!