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Taxinomic characterisation of cotton seeds (Gossypium ssp.) through morphological and morphometric analyses. Exploratory and archaeological approaches.

Milon J., Bouchaud C., Cucchi T., Viot C.. 2018. Las Palmas de Gran Canaria : s.n., 1 p.. International Workshop for African Archaeobotany - IWAA 2018. 9, 2018-06-26/2018-06-29, Las Palmas de Gran Canaria (Espagne).

Cotton (Gossypium sp.) includes four independently domesticated species: two diploid species, G. herbaceum in Africa and G. arboreum in the Indian subcontinent, and two tetraploid species, G. hirsutum in Central America and G. barbadense in Peru. The understanding of the diffusion history of these cottons is limited by the fact that the seeds, regularly found in archaeological context, cannot be determined at the rank of the species based solely on morphological observations. This study therefore explores the potential of morphometric, traditional and geometric analyses on modern seeds to extract a taxonomic signal that can be applied to archaeological material. The modern corpus is composed of varieties of the four domesticated species of cotton, cultivated in greenhouse (Montpellier, CIRAD) and in the field (Spain and Saudi Arabia). Specimens of herbarium seeds (MNHN) from the 19th and 20th centuries are also taken into account. The corpus is completed by archaeological seeds from the Sudanese site of Mouweis (Meroitic period, 1st-4/5th c. AD) and the Saudi site of Mada^'in Sa^lih (Nabateo-Roman period, 1st-4/5th c. AD). Because of the conservation by carbonization of archaeological specimens, experimental carbonizations were carried out on modern seeds in order to evaluate the impact of carbonization on the shape of the seeds. The shape of the modern and archaeological seeds was captured using two approaches. (1) A log shape ratio of linear measurements (traditional morphometric analyses) and (2) an outline analyses with a sliding semi-Landmarks approach (geometric morphometric analyses). These approaches discriminate diploid species from tetraploid species and differentiate species within the modern corpus. Seed carbonization does not affect this taxonomic discrimination and seems, on the contrary, to maximize taxonomic differences. The comparative approach seems to approximate the archaeological seeds to the species G. herbaceum without however affirming it clearly. These data offer new hypotheses on the dynamics of cotton circulation in Africa and the Arabian Peninsula during Antiquity.

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