The Natural History Museum site has a great facility whereby you can get a list of a particular postcode's native flora. There are pictures of most of them too so a sort of 'I-spy'-type treasure hunt could be organised, if one were so inclined.
Three-nerved Sandwort or Sticky Mouse-ear, anyone?
Sadly, although some of these local residents are very pretty in close-up, they are not deemed 'garden worthy'. Well, I beg to differ; some of them at least are certainly just a flower in the 'wrong' place.
My moment of glory was strolling along Trinity Street about 20 years ago spotted an odd looking plant, picked a stem took it home looked in various books and could not identify it so took it in to Baldwins where a very nice lady assistant said she had never seen anything like it before and offered to look it up later...If my archaic brain serves me well she said it was a Montia perfolatum(?) I think it was a member of the spurge family square stemmed as I recall.
I used to look at all the weeds growing on the walks to the school, still find my eye scanning the wilderness that passes for my garden now days!