As a horticulturist, I can spot a good plant app based on the accuracy and usefulness of its data and its content. This app presents in a very concise and useful manner tree identification information which has the Audubon Tree Guide beat. The reason I am giving this app 4 stars rather than 5 is because the range of inclusion isnt very broad. Like another reviewer said, it doesnt include many trees endemic to Florida as well as the Southeast. Id imagine this is also the issue with western trees.
PamaKane about Tree ID - TreeID with Fall Foliage, v2.6