A member of the pea family, there is much to like about the crown vetch. Its pinkish-purple and white blossoms are gorgeous and it adds nitrogen to the soil. The crown vetch is useful in erosion control.
There is a lot of bad with it. Crown vetch is an aggressive invasive plant--it crowds out native species. It also is toxic to horses.
In the 1950s crown vetch was planted on roadsides to prevent the aforementioned erosion. These plants were photographed in Morton Grove, Illinois' Linne Woods adjacent to the Dempster bridge over the North Branch of the Chicago River. I suspect this vetch patch was purposely planted decades ago.
Here's a close up.