Collected from small thorny trees abundant in the arid regions of the Western United States and as far south as Chile: Prosopis juliflora (Swartz) DC., P. dulcis Kunth., P. horrida Kunth., P. inermis H.B.K., P. glandulosa Torr., P. pubescens Benth., P. spicigera L., and other species of Prosopis, Leguminosae. Mesquite gum resembles acacia (gum arabic) in its physical and chemical characteristics. Review of structure work: F. Smith, R. Montgomery, The Chemistry of Plant Gums and Mucilages (Reinhold, New York, 1959) pp 175, 288-291.