We prove that there is a Hopf duality between two Hopf algebras built on ro
oted trees: the Connes-Kreimer Hopf algebra H-R which controls the renormal
ization in quantum field theory, and the Grossman-Larson Hopf algebra A int
roduced ten years ago through some 'differential' and combinatorial reason.
We then study two natural operators on A, inspired by similar ones introdu
ced by Connes and Kreimer for H-R.