Mines in overwintering rosette (can I call it that?) of an aster. For the plant ID, I think we're talking
Symphyotrichum sp. and specifically one of the heart-leaved asters, but I'm not sure so I placed a few images in the Plant ID help section:
Indoor batch rearing in progress
Looks like these start as linear and progress into a blotch. Two other examples from the same or nearby individual plants:
Adult from indoor batch rearing, 04/25/18