Over 500 Lactuca species are included in the International Plant Name Index (IPNI). However, as many of the species listed by IPNI refer to synonyms and basionyms, the genus Lactuca is generally considered to comprise about 100 species.
The primary genepool
The primary gene pool of lettuce is generally believed to consist of cultivated lettuce (L. sativa) and the sexually compatible species L. aculeata, L. altaica, L. azerbaijanica, L. dregeana, L. georgica, L. scarioloides and L. serriola.
The secondary gene pool
The secondary gene pool consists of L. saligna, while the position of L. virosa, either belonging to the secondary or tertiary gene pool, is still debated due to more complicated crossing barriers with cultivated lettuce.
The tertiary gene pool
The tertiary gene pool includes L. virosa, L. acanthifolia, L. aurea, L. longidentata, L. orientalis, L. quercina, L. sibirica, L. taraxacifolia, L. tatarica, L. viminea and L. watsoniana.
L. saligna, L. virosa and in particular L. serriola are the widest represented wild Lactuca species in genetic resources collections, and the widest used wild species in lettuce breeding. Basic characteristics such as chromosome number, life history, breeding system and global geographical distribution area are presented for the species of the lettuce gene pool in the downloadable overview that also contains a listing of the remaining Lactcua species with synonyms and basionyms where appropriate.