Trees. What are trees? Are they just stupid bits of wood? Or are they, in fact, wise and ancient beings that will outlive us all? Maybe they're both. Or neither. Maybe we're overthinking this. But with Guardians Of The Galaxy in cinemas this week, there's no doubt the humble tree has a glamorous new face: that of Groot, the walking, talking plank, as voiced by Vin Diesel, the walking, talking… well, you get it.