P.S. This morning, I went looking again for records of when/where I bought this plant. There is no email receipt, so I figured it must have been bought at the Quaker plant sale. The most recent catalog that I can find downloaded on my computer is from 2018, and it includes the "Burning Hearts" variety of Heliopsis helianthoides, and it calls attention to the purple-tinged leaves. I'm confident that this is it. :) I probably bought it when I last went in 2021.