One of America’s hottest cities and one of its coldest may have more in common than you would guess. In places like Phoenix and Minneapolis, scientists think that cities are starting to look alike in ways that have nothing to do with the proliferation of Starbucks, WalMart or T.G.I Fridays. It has to do with the flowers we plant and the fertilizers we use and the choices we make every spring when we emerge from our apartments and homes and descend on local garden centers.

“Americans just have some certain preferences for the way residential settlements ought to look,” Peter Groffman, a microbial ecologist with the Cary Institute of Ecosystem Studies in Millbrook, N.Y., recently told me. Over the course of the last century, we’ve developed those preferences and started applying them to a wide variety of natural landscapes, shifting all places — whether desert, forest or prairie — closer to the norm. Since the 1950s, for example, Phoenix has been remade into a much wetter place that more closely resembles the pond-dotted ecosystem of the Northeast. Sharon Hall, an associate professor in the School of Life Sciences at Arizona State University, said, “The Phoenix metro area contains on the order of 1,000 lakes today, when previously there were none.” Meanwhile, naturally moist Minneapolis is becoming drier as developers fill in wetlands.

In the Twin Cities, scientists have found distinct differences between the plants that grow in urban neighborhoods and those that grow in more rural settings. This doesn’t mean that in one place there are lots of potted geraniums and in another there are native tallgrass prairies. Rather, it turns out that what grows wild in the city is very different from what grows wild just a few miles away. Researchers from the University of Minnesota surveyed 137 yards in Minneapolis and St. Paul, looking at the plants that grew there spontaneously, and found that the yards held more exotic species than rural areas outside the city. Plants that came from much warmer climates were able to thrive there because cities, filled with heat-absorbing buildings and hard surfaces, are warmer than rural areas. They also found that the urban plants were more likely to be able to fertilize themselves, which was important in a place where growing spaces were separated by fences, streets and sidewalks. If you can’t find another member of your species, it’s handy to be able to breed with yourself.

Why does any of this matter to anyone who’s not an urban ecologist? “If 20 percent of urban areas are covered with impervious surfaces,” says Groffman, “then that also means that 80 percent is natural surface.” Whatever is going on in that 80 percent of the country’s urban space — as Groffman puts it, “the natural processes happening in neighborhoods” — has a large, cumulative ecological effect.