Oleaster (Olea europaea L. subsp. europaea var. sylvestris) is the ancestor of cultivated olive (Olea europaea L. subsp. europaea var. europaea) and it is spread through the whole Mediterranean Basin, showing an overlapping distribution with cultivated olive trees. Climate change and new emerging diseases are expected to severely affect the cultivations of olive in the future. Oleaster presents a higher genetic variability compared to the cultivated olive and some wild trees were found adapted to particularly harsh conditions; therefore, the role of oleaster in the future of olive cultivation may be crucial. Despite the great potential, only recently the need to deeply characterize and adequately preserve the wild olive resources drew the attention of researchers. In this review, we summarized the most important morphological and genetic studies performed on oleaster trees collected in different countries of the Mediterranean Basin. Moreover, we reviewed the strategies introduced so far to preserve and manage the oleaster germplasm collections, giving a future perspective on their role in facing the future agricultural challenges posed by climatic changes and new emerging diseases.

Algerian wild olives can represent an important resource for cultivated olive breeding, since they are characterized by great morphological variability. Moreover, they grow in different bioclimatic environments, including dry and hot climates, making the collections of wild olives a good source of abiotic stress resistance traits. Our study aimed to investigate the morphological diversity of 175 wild olive trees collected in North Algeria along with a wide range of different bioclimatic habitats for studying traits of olive accessions in relation to their different ecogeographical parameters. Wild olive trees were found in five different bioclimates areas spanning from humid to Saharan areas. They showed high variation in all traits, in particular fruit and stone weight, which expressed the highest coefficient of variation, and a high positive correlation between fruit weight/width. Cluster analysis separated the samples into two groups mostly based on fruit and stone size, while no relationship was observed with the area of sampling. Only the Saharan samples showed significantly different foliar and fruit characteristics compared to samples from other bioclimatic areas.

Hawthorn (Crataegus spp.) is a wild fruit tree of considerable ecological, nutritional, and medicinal value, widely distributed throughout the Mediterranean region and other temperate areas. Its taxonomy is particularly complex due to high morphological variability and frequent synonymy, which complicates accurate species identification. In Algeria, Crataegus spp. are very common, exhibiting substantial variability, especially in the northern part of the country. Despite its broad distribution, information on the genetic diversity of Algerian hawthorn germplasm remains limited. Characterization of this diversity is essential to support the identification of valuable traits of interest and to provide suitable genetic resources for the effective valorization and conservation of the species. In this study, 205 samples of Algerian wild hawthorn were characterized through an integrated analysis based on morphological descriptors and SSR markers, separating the samples into two well-defined genetic groups corresponding to C. azarolus (CA) and C. monogyna (CM) species. High levels of allelic richness, heterozygosity, and private alleles revealed substantial genetic diversity within both species. Overall, the integration of morphological and molecular data will provide a valuable basis for the conservation and management of Algerian hawthorn genetic resources.