Moss. My wife hates the stuff. She has spent hours removing it from between our paving stones. At one point, paving stones were the most popular way to pave driveways and patios in London, Ontario. The love affair is waning but some of us have stayed true. I think the moss looks great and I love the way it returns when pulled. When the world as we know it comes to an end, my guess is moss like this will outlast even the cockroaches.