How to Use this Key
The Urban Tree Key is a series of questions that work by the principle of exclusion: with each question, you exclude a bunch of species, shrinking the list of possible matches with each step. Each question includes two to four options; each option has a description and a photograph that illustrates the distinguishing characteristic. For each question, choose the option that most closely resembles the tree you are looking at and move to the next question. At the final stage, you are presented with a list of species and one characteristic for each that distinguishes it from the rest. Read each distinguishing characteristic and see if your specimen has it; if it does, check out the full description to be sure you have the right species; otherwise move on to the next.
Keep in mind that this first version of the Urban Tree Key only includes 45 species. On the streets of San Francisco alone, there are more than 200 species. If you get to the end without identifying your tree, go back over the questions to be sure you haven’t gone astray somewhere. If you’re still not having any luck, check out the Resources page for more information and sources for identifying species. Feel free to drop us a line if you come across a common species we’ve missed—we’ll work to include it in the next version.
What do you need to get started? In an ideal world, you would have the tree in front of you when you are using this key. Of course that’s not often possible, so photos and samples will have to do. You’ll need information about several parts of the tree, so if you’re using photographs, take an up-close picture of a leaf, a branch, the bark, any flowers or fruits, and the tree as a whole. Bring a leaf and, if possible, a fruit or flower, back to your computer with you, and if you find a branch on the ground bring it along too. Once you’ve used the Key a few times, you’ll get a feel for the kinds of tree traits that are included and you can focus on those.