This plant is in a wild blackberry patch that I am attempting maintain. The plant appears to be successfully competing with the blackberries (not winning, but not losing either - it is holding its own). This is impressive to me since blackberries are pretty invasive here in the US Pacific Northwest.
It was cut to the ground by me last fall (it is currently late spring) and I even attempted to remove roots. Some of them appear to have grown 3 feet in that time - not as fast as blackberries, but it appears to be more dense which could be why it is competing well.
The leaves remind me of maple, but it is not a tree. There are no spikes/thorns, and I have not seen any berries that I can recall. It is not woody - in fact the stems remind me of thornless blackberry primocanes but thinner.
I will add that I hadn’t seen them before till we cut all the blackberries to the ground two years ago an attempt to “start fresh” - that extra sunlight for a year seems to have helped them get a foothold.