There are trees busting through the nature-squelching asphalt of my neighbor's courtyard. When I walk to work, I see one growing right out of a sewer grate where one week prior there wasn’t even the faintest sign of life. They're everywhere in NYC, and seem to come from nowhere. They're all the same type of impossibly tough tree: the Tree of Heaven, a.k.a. ghetto palm, or as botany nerds would tell us, Ailanthus altissima.