The following key includes all the trees known to occur in Wisconsin outside of cultivation (native, naturalized and escaping from cultivation). It does not include species known only from cultivation, except for a few gymnosperms clearly identified as such, and it does not intentionally include shrubs. However, species of intermediate form and those variable enough to be considered either tree or shrub under certain conditions have also been included

Each page offers two alternatives. Select the choice which best suits the specimen at hand, click on the numeral to the right and you will be presented with another page with another set of choices. This process continues until you reach an answer. Photos used within the key are examples to illustrate the terms and may not match your specimen, especially early in the key where a given step may lie along the path to many subsequent species.