Vin Diesel found playing a tree ''challenging''.

The 47-year-old actor, who voices the Flora Collasus, Groot, in the new Marvel comic book movie 'Guardians of the Galaxy', struggled to portray the animated character without the use of facial expressions and movement.

He said: ''I play a unique extra terrestrial character. I play a tree. When the character was presented to me they prefaced it by saying this is the strangest character we've ever attempted to put on film for Marvel ... and it's a tree.

''For this one I felt like the thespian in me was being challenged.

''To be asked to play a role and not be able to use your facial mannerisms or body physicality to portray that role...''

In stark contrast to the part-animated comic book blockbuster, the 'Fast and the Furious' star is hoping to complete a historical film trilogy, based on the three Punic wars - fought between Rome and Carthage from 264 BC to 146 BC - which he has had in the pipeline for a decade.

He explained: ''As so many people know, I want to do this his historical piece. And I want to do the trilogy about the Punic wars it's still something that I have been working on the 10 years and it's something that has to be realised.''