Gray Thorn. Zizyphus obtusifolia, Buckthorn Family ( Rhamnaceae ), Gray Thorn. Also called Lotebush, Graythorn, Gumdrop Tree, and Texas Buckthorn. We wish to thank Wikipedia, the free encyclopedia for some of the information on this page. We share images and information with Wikipedia. A landscape shrub that will reach a mature size of about 6 feet tall by 8 feet wide. It's branches are waxy and gray - green, most branches end in a terminal thorn. It grows in shrubby and scrubby desert habitat, grasslands and prairie, woodlands, and other habitat types. It can be found among desert plants such as honey mesquite, smooth mesquite, ocotillo and creosote.[ The blue - black berries attract wildlife, it's thorns offer protection for nesting birds and other wildlife. The southern plains woodrat uses the twigs to build its houses. This plant was identified for us by Park Ranger, Scott Cleaves at the Gilbert Riparian Institute. Quick Notes: Height: About 6 - 8 feet. Flowers: The flowers are inconspicuous green - yellow flowers with 5 petals, in axillary cymes of 2 to 7 flowers. Flowering Time: June - July. Stems: Waxy gray - green stems with a terminal thorn. Fruit: It's blue-black berries are a wildlife attractant. Leaves: The leaves are shiny green leaves, 1/2 to 1 1/4 inches long , smooth to a slightly toothed margin. Found: The USDA claims it is native to the USA (AZ, CA, NM, NV, OK, TX, UT). In Arixona it is native to all counties except Navajo, & Apache. Also native to Mexico in Baja Norte, Baja Sur, Chihuahua, Coahuila, Durango, Nuevo Leon, San Luis Potosi, Sonora, Tamaulipas, Zacatecas, & Veracruz. Hardiness: USDA Zone 8a: to -12.2 �C (10 �F) USDA Zone 8b: to -9.4 �C (15 �F) USDA Zone 9a: to -6.6 �C (20 �F) USDA Zone 9b: to -3.8 �C (25 �F) USDA Zone 10a: to -1.1 �C (30 �F) USDA Zone 10b: to 1.7 �C (35 �F) USDA Zone 11: above 4.5 �C (40 �F) Soil pH requirements: 6.6 to 7.5 (neutral) 7.6 to 7.8 (mildly alkaline) 7.9 to 8.5 (alkaline) 8.6 to 9.0 (strongly alkaline) Sun Exposure: Full Sun Elevation: 500 - 5,000 Feet. Habitat: Washes, flats and canyons below 5,000 feet. Miscellaneous: Flowering Photos Taken At May 18, 2006 At Gilbert Riparian Preserve, Arizona.