Not yarrow, what is it? ID a plant

It's not yarrow. 99.9% odds on that. I can ID yarrow.
It's amok. It's early May, still too cold to plant tomatoes, and this stuff is hip high.
It's flowering, itty itty bitty flowers.
It's definitely not edible, I have tasted it multiple times, at various stages of growth. Still yuck.
It's eating my garden. If it's not a medicinal, I'm gonna have to cull it.
I don't want to cull them and then find out they were something awesome.
Zone 6 A/B, southern Missouri.
Help!
Pics should be able to be enlarged.

:D

Not yarrow. The board behind it is 24 inches high

Not yarrow. Ferny soft leaves

Not yarrow. It's flowering

Not yarrow. Look how TINY the blooms are!

Achillea millefolium grows up to 3 feet tall and the flowers can vary greatly in size...

Leaves taste bitter, (toxic to pets and horses), and can be invasive in the garden...

I visited my friend the other day and saw a plant that looked like that, also about hip high. I was very surprised to learn it was yarrow. The one I have stays short and hugs the ground. I wonder if it's a different cultivar or something? Or perhaps different conditions creating different growth habits?

Probably different soil, moisture, and sun aspect.

On a positive note it attracts butterflies!