Bulletin of the Torrey Botanical Club 102(6): 340-349 (Nov-Dec 1975)
Gossypium palmeri and a Polyphyletic Origin of the New World Cottons
B. L. Johnson

Fifty diverse collections of the commonly recognized tetraploid New World cotton species, G. barbadense, G. hirsutum, and G. tomentosum from South and Central America and the Caribbean and Pacific Islands gave identical seed protein electrophoretic patterns. Among 44 collections of the Mexican tetraploid G. palmeri, included in G. hirsutum, 6 gave patterns like that of the recognized species, while 38 gave a uniform but different pattern. The pattern of the commonly recognized species was simulated by electrophoresis of a mixture (1:1) of protein extracts from the Old World diploid cotton G. herbaceum (AA) and one of several wild American diploids (DβDβ) including the Peruvian G. raimondii and the Mexican G. lobatum and G. laxum. The palmeri pattern was simulated by a protein mixture (1:1) from G. herbaceum (AA) and the wild Mexican G. trilobum (DεDε). Other indigenous Mexican cultigens suggested that G. hirsutum may have originated from more than one primary amphiploid including G. palmeri (AADεDε) and one or more AADβDβ types. Transitional forms between indigenous cultigens and the cultivated G. hirsutum are abundant in southern Mexico, and intermediate forms between G. hirsutum and G. barbadense are widespread under cultivation. The protein pattern and the dispersion of morphological types favor the concept that G. barbadense (AADβDβ) originated in northern South America from G. herbaceum X G. raimondii and that the cultivated races of G. hirsutum represent various degrees of introgression involving G. barbadense and the Mexican hirsutum complex.

ANCIENT OR RECENT ORIGIN. According to the original hypothesis of Hutchinson et al. (1947) the New World cottons originated under cultivation from a fortuitous cross between an endemic American diploid and an Old World cotton carried across the Pacific by man. Gerstel (1953) suggested that alternatively a link across the Atlantic should be considered on the grounds that the African G. herbaceum rather than the Asiatic G. arboreum was the more probable Old World parent. Hutchinson (1962) pointed out that such a link implied an ancient origin of the New World cottons in eastern South America, whereas the D-genome species are confined to the Pacific coast.

Speculation regarding an origin of the tetraploids outside of the domain of the American diploid species must reekon with the evidence that G. barbadense and G. palmeri arose in close proximity with their respective putative D-genome parents. Arguments for an ancient origin must contend with the evidence that both of them arose after the differentiation of the present D-genome species, and that each tetraploid originated in a center of early American civilization.

A polyphyletic origin does not minimize the difficulty of accounting for the presence of G. tomentosum on the Hawaiian Islands. But, in the course of a tetraploid history of more than 4,000 years, it is not impossible for that species to have been transported from the Mexico-Central American area with the aid of man or ocean currents.

Cotton Bibliography

Wikipedia, "Archeological evidence from the Tehuacan Valley in Mexico shows the cultivation of this species [Gossypium hirsutum] as long ago as 3,500 BC, although there is as yet no evidence as to exactly where it may have been first domesticated. This is the earliest evidence of cotton cultivation in the Americas found thus far."

However, Wikipedia also notes: "The first clear sign of domestication of this cotton species [G. barbadense] comes from the Early Valdivia phase site of Real Alto on the coast of Ecuador (4400 BCE; calibrated radiocarbon dates) and from Ancon, on the Peruvian coast, where cotton bolls dating to 4200 BCE were found."

CybeRose note: So how and when did the Old World Gossypium herbaceum get to the New World to become one parent of these domesticated speciesd?