Almond species represent one of the most successful horticultural groups in the genus Prunus, Family Rosaceae. Classified to the subgenus Amygdalus, species occupy important positions in ecological habitats and include the commercially important tree crops: almond, peach, and nectarine as well as important rootstocks for almond, peach, nectarine, plums, prunes, and apricots. Almond has several wild types, including more than 40 species. It has been reported that these species were adapted and distributed to the increasingly xerophytic environments of Asia. Almond is one of the major nut crops in world production. The fruit and kernel have historically been an important source of food, as well as essences and oils used for making products ranging from medications to cosmetics. The almond wood is durable and fine-grained, making it valued for multiple uses, from woodworking to producing high-quality charcoal. In many regions, endemic almond species continue to play important ecological roles, including controlling erosion and acting as greenbelt filters for urban areas. The diverse germplasm possesses numerous traits of value for crop improvement, including improved resistance to biotic (pests and diseases) and abiotic stresses (drought, frost, and winter damage), as well as modified tree architectures and bearing habits. There also exists a long tradition for the use of this native germplasm as rootstocks for almond and other Prunus crops, particularly where tree size control and improved drought resistance are desired. Other traits useful for crop improvement include later flowering for frost avoidance, self-fruitfulness, and precocious cropping. Accurate assessment of genetic diversity and breeding value, however, depends upon a clear understanding of species properties and relationships. Gametophytic self-incompatibility in most species results in obligate outcrossing, enhancing both morphological and genetic variability within species. Because strong interspecific breeding barriers are not commonly present, considerable interspecies hybridization and subsequent introgression can also be found in the wild. While the resulting genetic and developmental uniqueness of almond and its wild relatives has resulted in it being classified in the genus Amygdalus in most European and Asian studies, this study also includes the more recent APG IV system of classification placing them within the genus Prunus.
