I don't remember any extended history of the Treehugger from Butler, the Quest is still not completed and the notice about it is still up on the board. When I go talk to him in town he asks me if i'm here about the bounty and then Nolan tells him we don't have all the Bony Plates. I haven't gotten any other dialogue from him and I haven't gotten a Tree Coin (idk if you can only get it if the Bony Plates quest is done or not).
I'm not sure if the Bony Plates are still dropped by Male Shellbeasts. I've only fought one recently and it didn't drop one, I've walked around in the plains near the tunnel to Coluna for awhile but I only found the one so far. I'll try to see if I can find more but if I don't at least it's not necessary to advance the main story so it's ok.
Thanks for looking into it though !