Nether Trees are trees that bring a little bit of the nether to the surface world. Nether Trees have netherrack for leaves and glowstone for the wood. Nether Trees DO NOT replace old trees. You won't have to go to the nether again (unless you want "Soulsand"). You should also try Nether tools by "Nuclearwar111". It goes great with Nether Trees.

Note: Planting a Sapling has a 25% chance of becoming a "Nether Tree"