Leafsnap is the first in a series of electronic field guides being developed by researchers from Columbia University, the University of Maryland, and the Smithsonian Institution. This free mobile app uses visual recognition software to help identify tree species from photographs of their leaves.
Leafsnap contains high-resolution images of leaves, flowers, fruit, petiole, seeds, and bark created by the conservation organization Finding Species. The Leafsnap app is available in versions for the USA and for the UK. It’s pretty good – try it – go to the iTunes app store and search for Leafsnap.