Good morning esteemed maple enthusiasts! We've been discussing in our office these growths or nodules on a maple leaf. I've seen them on bigleaf maple, and some naturalized sugar/bigleaf hybrids. One of the other arbs working in or office brought in a new sample the other day (photos attached.) I do not recall the specific reason for this. I do recall a group discussion at Royal Roads University some time back where we found some that were a good 1/4 inch long. General consensus was that they were not harmful, so the id on this associate has just gathered dust somewhere in the back of my mind. What are these and does anyone know why they happen?
From what I see in the pictures, I think it may be Maple bladder gall mite. http://oregonstate.edu/dept/nurspest/maple_bladder_gall_mite.htm
The leaf is Acer pseudoplatanus 'Atropurpureum' or one of the many other similar Acer pseudoplatanus cultivars with purple-tinged leaf undersides. Agree with Maple Gall Mite.
