SPR can be further divided into uSPR: Unrooted SPR, rSPR: Rooted SPR. uSPR is applied to unrooted trees, and goes like this: break any edge. Join one end of the edge (selected arbitrarily) to any other edge in the tree. rSPR is applied to rooted trees*, and goes: break any edge except the edge leading to the root node. Join one end of the edge (specifically: the end of the edge that is FURTHEST from the root) and attach it to any other edge of the tree.