Below are some photographs of strange growths on a patch of Asclepias syriaca I visited several weeks ago. From the few publications I’ve found, enations can be caused by viruses (Geminiviridae, Luteoviridae, etc.), and thus could be transmitted to nearby individuals via insect vectors or by the connected roots (milkweeds are clonal). Could be a genetic mutation, too, I suppose — could be spread by seed or via clonal growth. Anyone seen this before?
Photographed at Hildacy Farm Preserve in Media, PA.