I haven't read Peter Del Tredici's Wild Urban Plants of the Northeast: a Field Guide. I look forward to it; I love weeds....I love all plants. I just think it's dangerous to encourage the more aggressive ones. Maybe even in a city. I did watch with interest a thread on Garden Rant yesterday. I got the feelings that there are a lot of gardeners that think that the spread of these weeds is easily halted or maybe that there's some magic border at the edge of a city where the weeds will pause, look at the more natural pristine ecosystems and decide to respect them and stay in the city. Well....some of them will, but others, because of their vigor, adaptability, their type A personalities, will continue out into the world.
I live just outside Washington DC, a city that ought to get more credit for the beauty and extent of it's green spaces. Rock Creek Park, encompasses 1700 acres, a large park in a small city. Small creeks and drainages run off of Rock Creek so that there are thousands of homes and businesses whose backyards sit atop slopes that lead into the park. Take a walk downhill, or downstream, and it will rapidly become clear that the more aggressive weeds have, in many places taken over huge sections of the park. From here they move upsteam entering the wilder riparian spaces in Maryland. They do this because they can. Those abilities that allow them to survive the urban environment also allow them to rampage through natural areas. When they do this they often destroy the preexisting ecosystems.
The reason that I care about this is because the intricately co-evolved ecosystems they disrupt are wonderful in their complexity, their integration, and the beauty of their components and I love them. I suppose I'm just selfish to prefer Bloodroot, Hepatica, Spring Beauties, Pinxterbloom, etc. to monocultures of English Ivy, Kudzu, Japanese Honeysuckle, Lesser Celandine, Japanese Barberries, Bush Honeysuckle, and on and on.
It is true that many weeds only succeed in dry disturbed areas. These are the harmless curiosities that are fun to stumble on. We have been admiring a Giant Danelion for the past week at work. It's harmless enough in the Brickyard (the area where we compost and store mulch) but of course if, I should say when, the seeds get into the mulch it will gain entry to the collections and we'll have to deal with it.