If you've spent time out birding during the summer in the east, you may be familiar with Crown Vetch (Coronilla varia). This attractive member of the Pea family has been planted along slopes on highways and roadsides since the 1950s. Its strong root system helps prevent soil erosion and the pink/purple flowers are very attractive. Like many things, though, too much is never a good thing. Crown Vetch is native to the Mediterranean and has become invasive in many areas where it has been planted. It is very aggressive and will easily crowd out native plants in dune and grassland habitats. The plant has a "nitrogen fixing" ability whereby it helps replenish the nitrogen in the soil where it lives. This can adversely affect some native plants that may require infertile soil to grow.
All is not bad in Crown Vetch land. A small butterfly, the Wild Indigo Duskywing, has added the Crown Vetch to its list of caterpillar host plants. The prevalence of this plant has increased the population and expanded the range of this cryptic butterfly.
Many states have reduced or eliminated the planting of Crown Vetch. I'm sure enough has spread around to sustain the Wild Indigo Duskywing population for many, many years