A broad survey of available world literature showed that at least 98 wild Lactuca spp. (Asteraceae) have been described taxonomically. The distribution of the genus Lactuca worldwide includes 17 species in Europe, 51 in Asia, 43 in Africa, and 12 in the Americas (mostly the North American subcontinent). Species originating in Asia, Africa, and the Americas form ca. 83% of known Lactuca spp. richness; however, they are very poorly documented from the viewpoint of taxonomic relationships, ecogeography, and variability. The phytogeography of Lactuca spp. regarding their distribution on different continents and in relation to the structure of the lettuce gene pool is discussed. A more detailed analysis of geographical distribution and habitats is given for some species (L. serriola, L. saligna, L. virosa, L. perennis, L. quercina, L. tatarica), which represent the primary, secondary, and tertiary gene pools of cultivated lettuce (L. sativa). Original and synanthropic distributions of Lactuca spp. and their occurrence in natural and secondary habitats are discussed, along with the representation of wild Lactuca spp. in world gene-bank collections. Global biodiversity of Lactuca spp. and their representation in germplasm collections are poorly documented. Future studies of taxonomy, phytogeography, ecology, phylogenetic relationships, and genetic diversity are needed for a more complete understanding of this genus and taxonomically related genera.
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