Trees and shrubs can be identified by their woody stems. There are approximately 200 species of trees and shrubs in Grand Canyon National Park. Most of these are found in the higher elevations of the park, on the South and North rims. Some of the tree species include the white fir, Engleman spruce, blue spruce, Douglas fir, corkbark fir, ponderosa pine, Utah juniper, alligator juniper, Colorado pinyon, quaking aspen, Fremont cottonwood, Gambel oak, and Arizona walnut. Some of the shrub species have compound leaves and they include creeping barberry, fernbush, honey mesquite, catclaw acacia, creosote bush, boxelder, and New Mexican locust. Shrub species with simple and alternating leaves are the chokeberry, big sagebrush, seep willow, birchleaf buckthorn, netleaf hackberry, Utah serviceberry, and desert bricklebrush.