Bananas (Musa spp.) and plantains arise from the same types of plants, differing only in the amount of sweet sugar or blander starch in the fruits produced. Although often called "banana trees," the plants are actually tropical herbs that grow from fleshy underground roots called rhizomes or corms. Today there are hundreds of different bananas/plantains in existence because of mankind's selection and breeding to create plants with varying fruit sizes, colors and flavors as well as better resistance to plant disease.
General Plant Type
Banana plants are angiosperms (flowering plants) and are further characterized as monocotyledons, more commonly called monocots. Monocots have a single seed leaf, parallel leaf veins, no cambium layer and floral parts in multiples of three. The lack of a cambium layer in banana plants is the reason they technically cannot be called trees, even though some can grow 20 to 30 feet tall.
The banana is placed into the botanical family Musaceae, known simply as the banana family. Both banana and plantain plants are further grouped together into the genus Musa, separating them from the only other genus in the family, Ensete. Since Muscaceae is a family of monocots, other closely related families include the heliconia family (Heliconiaceae) and bird-of-paradise family (Strelitziaceae).
The Genus Musa
There are about 35 different species of banana/plantain in the genus Musa, with origins of all the plants being tropical southern and southeastern Asia and extreme northern Australia. Modern plants that produce edible fruits typically have lineage centering on the species Musa acuminata and Musa balbisiana.
According to the Species Profiles for Pacific Island Agroforestry, bananas were broken into five, now four, sections within the Musa family based on plant and fruit characteristics and/or region of nativity. The names of the current four sections are Australimusa, Callimusa, Musa and Rhodochlamys. Most edible bananas/plantains are from the sections Australimusa and Musa, while those plants regarded more as ornamental plants remain in Callimusa and Rhodochlamys.
Ploidy and Modern Breeding
Most edible bananas originate from two species in the section Musa: Musa acuminata (A) and Musa balbisiana (B). Complex hybridization of bananas leads to new plants, called culitvars, that typically have varying amounts of chromosomes from either of these two species. Ploidy refers to the number of chromosome sets (genome) in the cells of banana plants. The natural number of chromosomes is considered diploid, such as AA for Musa acuminata and BB for Musa balbasiana.
Genetic manipulation results in new plants that combine chromosomes from these parent plants. Triploid genomes (like AAB, AAA, ABB) as well as tetraploid types (AAAA, AABB, etc.) can be created. The vast majority of edible bananas worldwide today are triploids, according to the Species Profiles for Pacific Island Agroforestry. Interestingly, bananas with BB and BBB genomes do not effectively produce edible banana fruits.
Among the most name-recognizable bananas are those ambiguously called "Cavendish," which refers to a sizable number of plants with triploid genome (AAA). Cultivar names of plants in this group of edibles include 'Giant Cavendish,' 'Dwarf Cavendish' and 'Extra Dwarf Cavendish.' Another group of triploid bananas are those called "Pacific plantains" (AAB) and include cultivars like 'Pome,' 'Silk' and 'French.' In fact, according to Species Profiles for Pacific Island Agroforestry, the cultivar 'French' is commonly labeled as Musa paradisiaca, which is actually a hybrid derived from Musa acuminata and Musa balbisiana, not a species.