Purple Prairie Clover
Dalea purpurea
Notes:

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.

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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