Birdsfoot Trefoil Flower

The birdsfoot trefoil flower is dainty, roughly 0.5 inch/13mm in size.

Birdsfoot trefoil is a legume introduced to the U.S. from Europe. It's sold commercially and planted in grass-legume pastures, where it adds considerably to forage for grazing animals.  It spreads in prairie environments, which is where this photo was taken.