Purple Prairie Clover
Dalea purpurea

From what I've read, Clovers are one of the best caterpillar host plants. The adult pollinators also like them.

They are a legume. I try to protect them from the rabbits.

Till now man has been up against Nature; from now on he will be up against his own nature.
Dennis Gabor
Inventing the Future, 1964