Tree Explorer (leaf) and Tree Explorer (fruit) are apps that can be used to identify the species a tree belongs to by examining its leaves and fruits respectively. The app works by guiding you through a series of questions about the features of the leaves or fruits and then offers information about the identified tree species.

This process is a smartphone version of an identification key, a standard ecology tool used to identify biological entities through a series of steps. Each step narrows down the list of possible results, usually by asking a question about one or more characteristics of the entity being identified.

In the case of the Tree Explorer apps, you'll be asked a series of questions about the fruit or the leaves of the tree. This can range from a simple visual question  (e.g. does this tree have broad, flat leaves?), through generic questions (e.g. size) to more precise questions (e.g. type of "teeth" at the top of the leaves). Some trees can be identified with just a few steps, but others may require up to ten steps.

Once you've worked your way through the identification key, the app shows information about the identified tree species. A panorama view has pages for pictures (showing the full sized tree), description (Latin name, text description, tree products), leaf (picture and description of leaf characteristics), and fruit (picture and description of fruit characteristics). This information is usually enough to tell you whether you have made a correct identification.

The smartphone is the obvious device for this type of app, after all it's portability makes it the ideal field companion and it's more convenient (and easier to use) than the paper equivalent. It's probably fair to say that Tree Explorer is not a main stream app, but it does offer an intriguing glimpse of yet another way the smartphone can be a powerful tool... and for those curious about the world around them it's a fun and educational tool.

Marketplace description:

You see an unknown tree. Or perhaps have found part of a tree, and you want to know from what kind of tree it came. Often, you can identify an unknown tree by just one part, such as a leaf or a fruit. This application will lead you through qualities of leaves and fruits from the common trees.

Trees Explorer (leaf) and Trees Explorer (fruit), which have been published by Stanislaw Swierc, can be downloaded from the Windows Phone Marketplace for free.

The tree catalogue used in the identification key appears to assume that you are located in the US, but it may be usable elsewhere.