Do Cacti Have Roots?
All cacti have roots, and they perform a number of essential functions for the plants. Roots anchor cacti in soil, take up water and nutrients, and often store food and water in addition to the water stored in the plants' succulent stem tissues. Cacti roots' morphology varies from deep taproots to a network of finer roots that are near the soil surface and extend quite a distance. A cactus can survive for a period of time if it is severed from its roots, if its roots are damaged or if a stem cutting is taken, and new roots develop from tissues near the base of the plant or cutting.
Many cacti send down a long, strong taproot very soon after germinating. A taproot serves to anchor a plant from washing away in rainstorms and allows it to tap deeper subsurface soil layers with more moisture. Examples of these cacti are columnar cacti such as giant Mexican cereus (Pachycereus pringlei) and saguaro (Carnegiea gigantea), both large, treelike cacti of the Sonoran desert. Saguaro's taproot extends 5 feet into the soil. Giant Mexican cereus is hardy in U.S. Department of Agriculture (USDA) plant hardiness zones 9 through 10 and has multiple branches that can reach 50 feet tall. Saguaro is hardy in USDA zones 9 through 11 and has a single or branched stem reaching 30 to 50 feet tall.
In addition to taproots, cacti have lateral roots that branch repeatedly as they grow. Some cacti don't have taproots, instead relying on this network of roots to hold them in place and to harvest food and water. Saguaros have a massive array of fine roots within the upper 3 inches of soil so they can quickly absorb moisture from even light rains. A young saguaro only 6 inches tall was found to have a root system that filled a 6 1/2-foot area but extended only a little more than 3 inches into the soil.
Some cacti have the capacity to store food and water in succulent roots as well as in their stems. An example is Arizona queen of the night (Cereus greggii, formerly Peniocereus greggii), which is hardy in USDA zones 9 through 10 and has an enlarged root weighing 5 to 60 pounds. The part of the root that becomes enlarged is the secondary wood or xylem tissues, which store starch and water. The enlarged, fleshy taproots of the small, Chihuahuan Desert-living cactus Ariocarpus fissuratus shrink during drought periods, drawing the above-ground part of the plant below the soil surface. This cactus is hardy to 14 degrees Fahrenheit and endures Chihuahuan Desert summer temperatures of more than 100 degrees Fahrenheit, making it hardy in USDA zones 8 through 11. It is very slow growing and can be container-grown.
Most cacti do not have aerial, or adventitious, roots, but they are common on epiphytic cacti that grow among tree branches. They include orchid cacti (Ephiphyllum spp.) and night-blooming cereus (Hylocereus undatus). The fleshy roots emerge from the sides of the stems and help to anchor the climbing cactus stems to the trees or rocks supporting the plant. Aerial roots are in addition to the normal roots that are below the ground. Orchid cacti are hardy in USDA zones 10 through 11 and grown primarily for the large, brightly colored flowers of hybrid epiphyllums. Night-blooming cereus has large, white flowers and bright-red, edible fruits; it is hardy in USDA zones 10 through 11.
- Cacti: Biology and Uses; Park S. Nobel, Editor
- U.S. National Park Service: Saguaro Cactus -- Organ Pipe Cactus National Monument
- OnlinePlantGuide.com: Pachycereus Pringlei -- Giant Mexican Cereus
- OnlinePlantGuide.com: Carnegiea Gigantea -- Saguaro Cactus
- University of Texas: Mauseth Research -- Cacti: Root Succulence in Cacti
- Cactus Art Nursery: Ariocarpus Fissuratus
- Floridata: Epiphyllum Spp.
- OnlinePlantGuide.com: Hylocereus Undatus -- Night-Blooming Cereus, Dragonfruit
- U.S. Forest Service: Cereus Greggii Engelmann
- Jupiterimages/Comstock/Getty Images