Sebastopol's mysterious balls of leaves solved. It's mistletoe
Platanus orientalis. Sycamore. The fruit of the tree is patched. Green balls. Summer. Flowering of trees. Backdrop of sky and tree. Leaves of trees. Photos | Adobe Stock
Oak Galls and Mistletoe: Nature's Decorations - The Real Dirt Blog - ANR Blogs
Dr. Dirt: Galls cause little or no damage to host trees
Fuzzy Orange Galls from Parasitic Wasps on Oak Leaves – Observations from 2013-2020 – Naturalis Historia
Fuzz balls on my live oak tree are unsightly but not harmful. by Mary Reid Barrow - Lynnhaven River NOW