Limited by lack of water, shrubs and trees must disperse in order to survive. Once established, these desert plants are tenacious. Their roots will split rocks in search of nutrients, and many can live over 100 years. Shrubs and trees are distinguished by their height (a less reliable indicator in the desert) and the number of stems (shrubs have several). Common shrubs include Mormon tea, crucifixion thorn, creosote bush, four-wing saltbush, and cliffrose. Mormon tea contains psuedoephedrine, which is used in nasal decongestants. Many trees grow in the area, though most are limited to riparian areas where water is more plentiful. These include sycamore, velvet ash, black walnut, and Fremont cottonwood. Some tamarisk can be found and is a non-native species that can supplant native trees and significantly alter stream environments. National Park Service staff continue to remove tamarisk within the monument.