For a detailed discussion of bananas see http://www.hort.purdue.edu/newcrop/morton/banana
Wild Musa species
The genus Musa was traditionally classified into five sections (Ingentimusa, Australimusa, Callimusa, Musa and Rhodochlamys) but these have recently (2002) been reduced to three. Previously, the 2n = 20 chromosome species were separated into the sections Australimusa and Callimusa and the 2n = 22 chromosome species were separated into the sections Musa and Rhodochlamys. Recently, studies by Carol Wong and colleagues in Singapore have revealed that genetic differences between each section in the same chromosome group are smaller than those within each section. This means that the traditional separation of the sections can no longer be substantiated. Wong's studies do, however, maintain the separation between the 20 and 22 chromosome species. At present the 14 chromosome Ingentimusa section remains distinct.
Reference: Wong, S., Kiew, R., Argent, G., Set, O., Lee, S. K., and Gan, Y. Y., "Assessment of the Validity of the Sections in Musa (Musaceae) using ALFP." Annals of Botany 90 (2) : 231 - 238 (2002).
Ingentimusa section - from Papua New Guinea
Callimusa section (incorporating Australimusa)
Musa section (incorporating Rhodochlamys)
A number of distinct groups of edible bananas have been developed from species of Musa. By far the largest and now the most widely distributed group is derived from Musa acuminata (mainly) and Musa balbisiana either alone or in various hybrid combinations. The next but much smaller group is derived from members of section Callimusa (previously classified as Australimusa) and is restricted in importance to Polynesia. Of even more restricted importance are small groups of hybrids in Papua New Guinea; a section Musa group to which Musa schizocarpa has also contributed and a group of section Musa x section Callimusa (previously classified as Australimusa) hybrids.
From the time of Linnaeus until the 1940's different types of edible bananas and plantains were given Linnaean binomial names, such as Musa cavendishii as if they were species. In fact, edible bananas have an exremely complicated origin involving hybridisation, mutation and finally selection by humans. The giving of species names to what are actually very complex hybrids led to endless confusion in banana botany. In the 1940's and 1950's it became clear that the cultivated bananas and plantains could not usefully be assigned Linnean binomials. An alternate genome-based system for the nomenclature of the section Musa bananas was devised.
As mentioned above, the main group of edible bananas are derived from Musa acuminata and Musa balbisiana. As an example of the application of the genome based nomenclature system, the plant known by the "species" name Musa cavendishii became Musa (AAA group) 'Dwarf Cavendish'. The "new" name shows clearly that 'Dwarf Cavendish' is a triploid, with three sets of chromosomes, all derived from Musa acuminata designated by the letter "A". When Musa balbisiana is involved the letter "B" is used to denote its genome. Thus the variety 'Rajapuri' is correctly written as Musa (AAB group) 'Rajapuri'. 'Rajapuri is also a triploid with two sets of chromosomes from Musa acuminata and one from Musa balbisiana. In the edible bananas genome combinations such as AA, BB, ABB, BBB and even AAAB can be found.
No such nomenclature system has been developed for the next group of edible bananas derived from section Callimusa (previously Australimusa). However, this group is known generally as the "Fe'i" or "Fehi" bananas and there are numerous cultivars of this group in the South Pacific region. They are very distinctive plants with upright fruit bunches (edible banana bunches normally hang down) and feature in three of Paul Gauguin's paintings. The flesh must be cooked before eating, is bright orange and can colour the ingestor's urine. The Fe'i bananas are no longer very important for food, although some have ritual significance. It is probable that the Fe'i bananas derive mainly from Musa maclayi although their origins are not as well understood as the section Musa bananas. Varieties can be formally named as in this example, Musa (Fe'i group) 'Utafun'.