After scrolling through the May thread I know I am in the right place to get this plant identified. It was grown by Sunny Border Nurseries right here in CT. I checked their website, but they have at least 100 species listed in their "alpines" category and not all have photos. I looked at 15 or so "A" species and lost patience...I thought this looked like a type of Sanguisorba, but the flower seems to be wrong. Any help is sincerely appreciated.
Unknown alpine/rock garden plant
It's an Acaena, not sure which species... possibly Acaena inermis.
Thanks! Beth Chatto has a nice photo here: