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By Kathleen Perricone

For Vin Diesel‘s latest role, in Guardians of the Galaxy, the actor really had to step outside his comfort level … to play a tree with abs of steel named Groot.

“Can you believe even my tree has abs?” he joked when he called in to On Air with Ryan Seacrest on Wednesday morning. “I’m a flora colossus. I’m a monarch on Planet X …”

All joking aside, Vin insists, “It is kind of cool to be challenged enough to play a character … I’ve been acting all my life and I don’t think the thought ever crossed my mind that someone would ask me to play a three-word monosyllabic tree. It was kind of a cool challenge because anyone who has read the comics … he actually says a lot of different things … and those who are oblivious to the nuances to his speech can hear ‘I Am Groot.’”

Also up next for Vin is Fast & Furious 7, which is expect to be released April 3, 2015. Of course, finishing the movie was especially difficult once co-star Paul Walker passed away during filming.

“It started out as the easiest movie because it was our seventh film, and then of course it became the hardest film to shoot,” explains Vin.

Guardians of the Galaxy is in theaters this Friday!