Results/Conclusions . Most studies have shown that great cacti are ecologically important. They provide abundant nectar, pollen and fruits that sustain high densities of bats, birds, and insects, maintaining a unique food chain in many ecosystems. Great cacti serve as refuge for many animals that make their nests in their branches, use their shade, and burrow in the skeletons of dead cacti. All these positive interactions contribute to the diversity of dryland ecosystems. Many human groups, especially in drylands, enshrine great cacti as central elements of their culture, incorporating them into their material and spiritual world. They use them for food and for construction materials. Many species have medicinal and therapeutic uses, and play a central role in their mythology. However, hard data on their economic and social importance is limited. It is therefore urgent to quantify traditional forms of fruit harvesting and timber use, and their impact on local human populations. Formal modern studies of giant cacti started in the USA, but the research impetus have slowly shifted towards research groups in Latin America. Most research includes population dynamics, ecological facilitation, plant physiology and seed germination, horticulture, and interactions with pollinators. Cacti hold key information on how to cope with extreme environments. Current genomic studies using the giant saguaro cactus will help unraveling the complex phylogeny of the group, as well understanding better the role of regulatory genes and metabolic networks involved in the specialized CAM photosynthesis, nutrient transport, and water economy. The ongoing land-use change and rampant illegal trade of live cacti and their seeds urge for the protection and documentation of the population dynamics and the interactions with other organisms of extant populations.
