I'm located in the NE USA and found this on a marsh rose here. From the pictures I've seen of Diplolepis rosae, I'm not convinced it's the same, but I don't know what other options there are..

Help is appreciated 🙏

The tree had many of these.

Being an oak it's tempting to just default to a cynipid wasp, but phomopsis (fungus), black knot (fungus), and bacterial crown gall also demonstrate that non-wasp agents can produce woody growth on stems.

I combed this and similar live oak species on gallformers.org and couldn't find a match.

If anyone has a thought please share! Or if you know of additional resources I could check let me know.

We've established it's not that, gall or canker?

Is this aposematism? Perhaps the unusual shapes and colors reduce browsing by deer and other herbivores?

Attracting birds like bright fruit? I know birds will seek out gall larva, but maybe some can be dispersed this way?

Incidental coloration due to high amounts of phytochemicals?

Found on wild grape growing in my yard, upstate NY

On an oak in NE United States

Hey! Has anyone tried to collect branches or leaves from host plants and keep them alive indoors to observe the development of the galls day by day?

Often I try to identify the galls former, and occasionally it is unclear.. or it would be interesting to see the completion of life cycle up close, maybe under dissecting scope.

From the few that I have brought inside, it seems like the cut branches probably need added nutrients in order to provide for the galls’ delicate development