Possibly Gunnera manicata.

I'm thinking this may be Astilboides tabularis. Judging by the size of the Alchemilla mollis leaves alongside it is not big enough to be Gunnera manicata. Nor it it jagged edged and prickly. And the flowers don't fit Gunnera either.

Yes, Astilbiodes.

Yep. Gunneras produce dense conical heads beneath the leaves, and would have to be coddled to live through Maine winters.