At one point the entire planet of Gren was set on fire.
Gren is the second closest planet to the sun, but also one of the slower moving planets. When one of the Wood Alignment is in proper alignment it will be maintain it's aura for a considerable amount of time compared to Razen.
Gren's name most likely comes from the colour green, as a lot of the planet seems to be this colour. It could also come from the Danish word 'Gren', meaning branch, which would relate to it's vast amount of plantlife, and the Wood Element.