You should include some pictures with your question here; that always helps the crowd.
That said: you posted on another forum with same question plus a picture. I'll copy my answer here.
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I think you have a mimic there.
Ural False-spirea -
Sorbaria sorbifolia is very cold hardy, but not known for being excessively showy. It makes its best use as a spreading/colonizing ground cover with fine/feathery foliage habit.
Ural False Spiraea (Sorbaria sorbifolia)
