You can identify a shrub's species yourself by using a taxonomic or dichotomous key. Taxonomic keys use details such as branch patterns and leaf shapes to identify species. You can also show a picture of the shrub to a botanist or horticulturist.
If you are not able to take a physical sample of the shrub, collect as much information as possible about the plant's physical characteristics. Note leaf shape and size. Count the number of leaves attached to each twig, and notice whether the leaves are in pairs or alternating. Sketch the branch pattern and any patterns present in the bark or leaf veins. Notice any flowers or fruit, as they are valuable identification aids.
Use a taxonomic key that covers the geographic region you are interested in, as well as the plant type. Once you have noted all the physical characteristics of the plant, use the choices in the taxonomic key to complete the identification process. Dichotomous keys allow you to address only one characteristic at a time, while polyclave keys let you enter multiple characteristics for faster identification. Many electronic keys for cell phone or computer are polyclave.
Photographs are also helpful for identification. Place a coin or ruler in the background for scale, and take pictures of both leaves and stems. If there are both young and mature shrubs present, photograph both.