Nomenclature system for edible bananas

The informal nomenclature system used to classify banana cultivars was developed by Norman Simmonds and Kenneth Shepherd in 19551 . It forgoes two-part Latinized names (the first part indicating the genus, and the second one the species) and instead classifies edible bananas into genome groups, according to the relative contribution of their ancestral wild species, and into subgroups, sets of closely related cultivars. This system eliminates almost all the difficulties and inconsistencies of a taxonomy based on Musa paradisiaca and Musa sapientum2 .

However, due to difficulties in assigning certain cultivars to a genome group and subgroup, there are inconsistencies in the way the system has been applied. Contributing to the confusion is the continued use of Latin binomials to refer to edible bananas. 

Simmonds and Shepherd's genome-based system

In this system, bananas, at least the ones that are related to Musa acuminata and Musa balbisiana, are classified according to the relative contribution of these species designated by the letter A, for acuminata, and B, for balbisiana. A cultivar is assigned to a genome group according to the number of chromosome sets in its genome (its ploidy) and the species that donated them (see Domestication of the banana). Diploid cultivars can belong to the AA or AB genome group, while triploid cultivars fall into three genome groups: AAA, AAB and ABB (see the cultivar diversity portal).

Some taxonomists recognize a BBB genome group, but its existence has not been conclusively demonstrated. Tetraploid cultivars are mostly hybrids produced by breeders.

Genome groups are further divided into subgroups usually defined as a set of cultivars derived from each other through somatic mutations. On the basis of this system, cultivar names are put between inverted commas and preceded by the name of the genus and when known, the name of the group and subgroup. For example: Musa (AAA group Cavendish subgroup) 'Robusta'3 . 

Scoring system

The system is based on 15 characters that were chosen because they are different in Musa acuminata and Musa balbisiana1 . Each character is scored on a scale from one (typical Musa acuminata) to five (typical Musa balbisiana). The possible total scores range from a minimum of 15 to a maximum of 75. The expected scores are 15 for AA and AAA, 35 for AAB, 45 for AB, 55 for ABB and 75 for BB.

Character	Musa acuminata	Musa balbisiana
Pseudostem colour	More or less heavily marked with brown or black blotches	Blotches very slight or absent
Petiole canal	Margin erect or spreading, with scarious wings below, not clasping pseudostem	Margin inclosed, not winged but clasping pseudostem
Peduncle	Usually downy or hairy	Glabrous
Pedicels	Short	Long
Ovules	Two regular rows in each loculus	Four irregular rows in each loculus
Bract shoulder*	Usually high (ratio<0.28)	Usually low (ratio>0.30)
Bract curling	Bracts reflex and roll back after opening	Bracts do not reflex
Bract shape	Lanceolate or narrowly ovate, tapering sharply from the shoulder	Broadly ovate, not tapering sharply
Bract apex	Acute	Obtuse
Bract colour	Red, dull purple or yellow outside; pink, dull purple or yellow inside	Distinctive brownish-purple outside; bright crimson inside
Colour fading	Inside bract colour usually fades to yellow towards the base	Inside bract colour usually continuous to base
Bract scars	Prominent	Scarcely prominent
Free tepal of male flower	Variably corrugated below tip	Rarely corrugated
Male flower colour	Creamy white	Variably flushed with pink
Stigma colour	Orange or rich yellow	Cream, pale yellow or pale pink

*x/y

Formalizing Simmonds and Shepherd's system

Efforts to classify cultivars into genome groups and subgroups have not progressed much since Simmonds's extensive treatment of cultivars in Bananas. Recognizing the limitations of the current system, some ProMusa and MusaNet members are discussing aligning Simmonds and Shepherd's genome-based nomenclature system with the International Code of Nomenclature for Cultivated Plants as part of an effort to have it formally recognized4 .

References

See also on this website

Further reading