In the past the field guide was printed. The more extensive the guidebook, the heavier it was to carry through the woods. Many people stayed at their homes. If they went out into the woods and saw the odd or unidentified plant they told themselves they'd remember its attributes and search it out in the future. They did not .Then plant identification websites came the smartphone revolution. Initial reference apps provided an easy-to-carry option to books. However, they came with some of the same disadvantages like printed books. They usually only had one photo of a species. They usually relied upon the system of binary keys to determine species which required that users be able to access multiple areas within the plants.
Today, there are applications that utilize the power of smartphones to accomplish something that was not possible in the past: identify species by simply taking a picture. Lily Plant was the pioneer, and continues be an excellent resource. But it's only of use during winter. Many companies have taken the technology to allow precise identification even from simple snapshots of the tree, branch or leaves. This is done by using a comparison of an image with "deep learning" databases.