Characterized by an abundance of pavement, reflected heat, polluted air and contaminated soil, our cities and towns may seem harsh and unwelcoming to vegetation. However, there are a number of plants that manage to grow spontaneously in sidewalk cracks and roadside meridians, flourish along chain-link fences and railroad tracks, line the banks of streams and rivers, and emerge in the midst of landscape plantings and trampled lawns. On their own and free of charge, these plants provide ecological services including temperature reduction, oxygen production, carbon storage, food and habitat...