Mulberries (Morus spp., Moraceae) are deciduous trees with a long history of domestication and selection for sericulture. In Europe, the earliest mulberry species introduced was Morus nigra L., native to western and southwestern Iran. M. nigra thrived in the Near East and Europe at least since the Iron Age and Roman times, as documented by literary sources and archaeobotanical records. This predates the widespread establishment of M. alba L., which was introduced from East Asia into the Mediterranean Basin with the expansion of sericulture, probably between the ninth and twelfth centuries. Thereafter, M. alba was gradually promoted in late Byzantine era and expanded markedly from the sixteenth century onward, reaching its golden era of cultivation during the eighteenth and nineteenth centuries, when sericulture flourished across most European countries. The widely distributed “Filippine” variety, taxonomically treated as M. multicaulis (M. indica var. multicaulis) and historically reported as imported via the Philippines, entered the European cultivation in the early nineteenth century (often cited around 1825) and is commonly placed within the M. indica genetic background. Additional high-leaf-yielding varieties associated with the M. indica complex, frequently referenced under traditional (variety-level) names such as latifolia, kagayamae and bombycis, were introduced from Japan between the 1930s and 1950s. In recent decades, hybrids involving M. rubra of the American origin have also been introduced to Europe, primarily for fruit production but in some cases also considered for sericultural use.

From a sericultural perspective, the most important genetic background is concentrated in the white mulberry (Morus alba sensu lato) and the Indian mulberry ingroup (Morus indica sensu lato), which together underpin most traditional and modern high-leaf-yield varieties. These ingroups are taxonomically and genetically complex because mulberries exhibit pronounced phenotypic plasticity (notably leaf heterophylly), variable sex expressing systems (monoecious or dioecious, including variations among genotypes) and extensive cytogenetic diversity (ploidy ranging from predominantly diploid and triploid cytotypes in M. alba to docosaploidy in M. nigra). Moreover, frequent spontaneous hybridisation as well as targed genetic recombination through breeding programmes blurred boundaries among species and on lower taxonomical level. Historically, mulberries were often propagated generatively (by seeds), which increased genetic variation as well as within-region diversity. In warmer regions of Italy and the former Austro-Hungarian monarchy, grafting of high-performing genotypes has been more common since late 18^th century.

Consequently, morpho-phenological traits alone are frequently insufficient for reliable cultivar identification, even when detailed morphological descriptors are applied. Moreover, this biological and taxonomic complexity directly affects how genetic resources should be conserved, how planting material is maintained and propagated, and how mulberry breeders  and growers select genotypes suited to local climate and management conditions. In response, best practice increasingly combines standardised morphological cataloguing supported with molecular tools to resolve uncertainties at lower taxonomic level, identify synonyms, and support robust selection and conservation decisions.

A specific challenge for the taxonomic positioning of the mulberries presented in the ARACNE mulberry catalogue is that many varieties are recorded under traditional names and synonyms (syn.) that have been applied historically to taxa now treated under different accepted scientific names and taxonomical level. In addition, many modern sericultural varieties originate from simple or complex crosses (spontaneous and/or artificial breeding) among M. alba, M. indica and M. rubra. Accordingly, most varieties associated with M. alba and M. indica are treated as sensu lato (s.l.; “in the broad sense”), whereas putative M. rubra accessions are provisionally assigned as M. rubra confer (cf.). The qualifier “cf.” indicates that most diagnostic characters correspond to M. rubra, but some are ambiguous; identification is therefore provisional and expected to be resolved through comparison with reference material. The genetic relationships of the catalogued varieties  are currently being analysed within the ARACNE project.