Classification of the Genus Nicotiana and Origin of Nicotiana Species

In the eighteenth century, Linnaeus was the first to describe four species of Nicotiana. The first attempts to systematize the growing number of new Nicotiana species were made by the nineteenth century botanists Don and Setchell. Kostoff significantly expanded the existing systematics, and the work was crowned by Goodspeed’s modern classification published in mid-1950s. The subsequent revision of Goospeed’s systematics was proposed by Knapp. Drawing largely on data from advanced molecular studies, Knapp introduced several major changes to the universally recognized Goodspeed’s taxonomy. Since Goodspeed’s times, many new species have been added. They include the early additions mostly from Australia and the only non-Australian member of the section Suaveolentes discovered in south-western Africa, four new species in the section Alatae, and one species in each of the sections Paniculatae, Noctiflorae and Tomentosae, ending up with the most recent influx of 24 new Australian species, all classified in the section Suaveolentes. A list of the recognized or provisionally described species, totalling 108 items, provides information on author/authors of the description, continent of origin, year of first description, diploid chromosome number and genome size. The subsequent part reviews the evolution of the genus with special attention to the origin of the cultivated tobacco, Nicotiana tabacum. Early nineteenth century views on the ancestry of N. tabacum are presented followed by the discussion of how the combination of cytogenetical, biochemical and molecular evidence has led to the present theory according to which N .tabacum takes its origin from the spontaneous cross of some ancestral forms of N. sylvestris and N. tomentosiformis, possibly with subsequent introgression from N. otophora. The review ends up with a brief discussion of the origin of several other allopolyploid species, including N. rustica, N. arentsii and some others.