Circular brown spots with surrounding circle of yellow or light green, showing on both sides of the leaf, 1-3 mm. in diameter. Not uncommon on leaf of tulip tree, Liriodendron tulipifera.
”- FA Stebbins: (1910) Insect galls of Springfield, Massachusetts, and vicinity©
Reference: https://www.biodiversitylibrary.org/page/21941240#page/37/mode/1up