Organic matter absorption
Groot can absorb wood as food, with the ability to rebuild himself and enhance his strength. He can control trees, using them to attack others, and also appears to be resistant to fire. He is able to sprout, massively increasing his mass but also severely inhibiting his movement.
Groot's tree like form provides him great strength limited only by the amount of wood he is able to absorb.
Groot's hide is composed of wood dense enough and durable enough to make him immune to most conventional weapons, including gunfire and fire which would consume most woods.
Groot can animate and command trees and plants, capable of even ordering a whole forest to uproot itself as an improvised army.
Groot has been seemingly killed on three occasions, each time regrowing from a sprig.
Due to Groot's lineage, coming from an ancient and ennobled sap-line and being the scion of an elite royal house, Groot has received the finest education from the most gifted of tutors. He is highly intelligent and has a tremendous grasp of quasi-dimensional super-positional engineering.
Groot has shown the ability to create multiple miniature copies of himself known as cuttings which retain all his memories and can be used to resurrect himself if he is destroyed. Cuttings can also germinate other plant life forms so Groot can control them.