Securigera varia, or Crown Vetch, is probably one of my favorite weeds.
I used to relish seeing it each while driving back and forth from Blacksburg, Virginia (where I studied horticulture at Virginia Tech) and my parents' place near DC. Though it can be invasive, the sprawling legume does a good job of controlling erosion on the steep hillsides that go hand-in-hand with highway construction. Along I-81, these roadbanks were coated in the purple flowers from June through August, always indicating that summer - real summer, complete with hot, hot days - had arrived.
I wanted to write about why this plant had been given the moniker Crown Vetch, but unfortunately the information is sparse (at least online info). From what I can dig up, the previous genus for Securigera was Coronilla, meaning Corona or Crown. Vetch is a common name for another Fabaceous genus, Vicia. Vicia faba, incidentally, is the Fava Bean. So I can break down the actual Latin for the common name, but how it was applied to Securigera, I can't really say.
A few other photos of wildflowers (or weeds, depending on your perspective) are below.
Red Clover, or Trifolium pratense:
Oxeye Daisy, or Leucanthemum vulgare: