I collected a sprig of Bog rosemary, Andromeda polifolia at Big Lake, Washington county, with a fellow amateur botanist in June 2025. We were unsure about what was causing the unusual pink growth and leaf form on our specimen, so we consulted Glen Mittelhauser (MNHO) and Gary Fish (State Horticulturist) who each identified the same fungus as responsible for this presentation. The Exobasidium fungus generates abnormal growths (galls) in the tissue of shoots, leaves and flowers of the host plant, in this case Andromeda polifolia (Bog rosemary). It is known throughout north temperate regions, especially peatlands. It is similar tot he azalea apple or gall. My fellow plant nerd who collected it with me had already bet her money on fungus or bacteria as a solution, and she was absolutely right! Impressive, indeed. I'm thrilled to have had this confirmed and explained. The world makes sense again, thanks to Glen and Gary.
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