Redpower Rubber trees are large sprawling trees generated by the Redpower mod. The wood it drops can be crafted into 8 sticks, and placing it in an Extractor from the IndustrialCraft mod will yield rubber.
Redpower Rubber trees cannot be set on fire, so this makes the incredibily difficult to destroy if you have spawned in that area unless an item such as a Dark Matter Axe is used.
Also, due to the tree's enormous size, they can block out a lot of light from the sun. If there is a cluster of them, they can start spawning aggressive mobs under them.
Rubber tree leaves must be right next to a rubberwood block or otherwise they will decay. This differs from the normal trees' 3 block radius.