There have been questions such as "what species is Groot" but what I'm wondering is what exactly he is. He appears obviously to be simply wood, but he is an alien creature not from Earth and never catches fire or anything. Plus, in Avengers: Infinity War Baby Groot
cuts off his arm to hold Thor's new ax. This doesn't burn through and is surprisingly durable, despite Groot seemingly being just wood.
And in Guardians of the Galaxy,
Groot wrapping himself around everyone helps them survive an explosion, something normal wood would likely be unable to do.
Does this have anything to do with his species? Is he just alien wood?