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Carpological analysis of Phoenix (Arecaceae): contributions to the taxonomy and evolutionary history of the genus

Diego Rivera, Concepción Obón, Joaquín García‐Arteaga, Teresa Egea, Francisco Alcaraz, Emilio Laguna, Encarna Carreño, Dennis Johnson, Robert Krueger, José Delgadillo, Segundo Ríos
Botanical journal of the Linnean Society 2014 v.175 no.1 pp. 74-122
Arecaceae, biogeography, seeds, type collections, Persian Gulf, Turkey (country)
The main purpose of this study was, first, to analyse the morphology of seeds of Phoenix spp. and relevant cultivars and to assess the taxonomic value of the information generated as a means of studying the systematics and evolutionary history of the genus Phoenix. We then analysed seed morphological diversity in P. dactylifera, supported by morphotypes shared with fossil and/or archaeological materials, to advance the knowledge of the origins, history and biogeography of one of the most important cultivated palm species. The other objective was to develop a methodology for assigning different commercial seed samples and archaeological materials to determined morphotypes as a tool for their identification at the species level. Three hundred and sixty‐four seed samples (3920 seeds) were analysed: 304 samples of modern Phoenix spp. (including five herbarium type specimens and eight type icons), 51 archaeological samples and nine fossil seed samples and subsamples. Information was systematized in a crude matrix with 364 units representing seed samples and 67 descriptors. Descriptors are frequencies, in percentage, for each of the 41 qualitative states and of the 26 classes that were recognized for the quantitative parameters. Analyses proceeded sequentially, starting with modern samples consisting of type specimens and botanically verified specimens. Eight species show characteristic seeds and are clearly assigned to morphotypes [P. acaulis, P. canariensis s.s., P. paludosa, P. reclinata, P. roebelenii, P. rupicola, P. sylvestris and P. theophrasti (excluding populations from Datça, Turkey)]; the other taxa are not clearly separated on the basis of the seed morphology alone. In parallel, fossil and archaeobotanical samples were analysed. There is no clear separation between fossil and archaeological samples, between different periods of the archaeological samples or geographical origins. Combination of modern, fossil and archaeological seed results in the same analysis revealed that it is possible to allocate archaeological and fossil materials to morphotypes shared with modern living Phoenix spp. All archaeobotanical samples could be classified in groups with modern seed samples. The assignment of archaeobotanical samples was made, mainly, to morphotypes of P. dactylifera. However, some samples were assigned to morphotypes of P. reclinata, P. caespitosa, P. atlantica, P. theophrasti, P. pusilla and P. canariensis. Archaeological seeds were not allocated to group 19, containing the samples of P. sylvestris, P. iberica and the Miocene fossil P. bohemica. It appears that species such as P. theophrasti, P. canariensis, P. caespitosa and P. reclinata formerly had a much wider area of distribution. The morphology of two of the three Eocene samples (Phoenicites occidentalis and Phoenix hercynica) is that of P. dactylifera. Attribution and dating of these samples need to be carefully reviewed. Apparently the great diversity of P. dactylifera date morphotypes during the Neolithic was followed, during the Chalcolithic and the Bronze Age, by a remarkable constriction (bottleneck) in terms of morphological variability, which slowly recovered from the Iron Age onwards. With the currently available evidence, we cannot exclude a group ancestral to P. dactylifera in the Persian Gulf, related to the eastern chlorotype. In parallel, another group ancestral to P. dactylifera may exist in the western Mediterranean, including P. iberica, related to the western chlorotype. © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175, 74–122.