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

Abstract

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 th...

Long and attenuated: comparative trends in the domestication of tree fruits

“…Recent genetic studies suggest deep divergence in the genomes of date palms from the central and western Sahara, and north Africa (Hazzouri et al 2015), raising the possibility of a second centre of domestication, as yet unsupported archaeologically, or a process of introgressive capture (sensu Larson and Fuller 2014) from now extirpated wild palms in the Sahara, perhaps represented by remnant populations on Djerba and Kerkennah islands of Tunisia (Zehdi-Azouzi et al 2016) and by P. atlantica on Cape Verde Islands (Henderson et al 2006). The Mediterranean sister species, P. theophrasti appears to be a true wild species, now extirpated from its former distribution in the Levant, where it was recorded from sixth millennium bc finds in southern Israel (Kislev et al 2004), the identity of which is confirmed by geometric morphometrics (Rivera et al 2014;Gros-Balthazard et al 2016). Middle Holocene finds are restricted to Arabia, Pakistan, Mesopotamia and the Levant, whereas reports from the Nile Valley occur in the early second millennium bc (i.e.…”

“…All specimens in the UCL archaeobotanical reference collection; scale bars 1 cm that wild and domesticated populations fall towards different ends of a morphological spectrum seems clear. Indeed, studies employing geometric morphometrics (GMM) on grapes (Vitis vinifera) (Pagnoux et al 2015;Bacilieri et al 2017), as well as on other taxa such as olives (Olea europaea) (Terral et al 2004;Newton et al 2014), plums (Prunus domestica) (Ucchesu et al 2017) and dates (Phoenix dactylifera) (Rivera et al 2014;Gros-Balthazard et al 2016), which factor out size and focus instead on shape, demonstrate statistically shape differences between wild and cultivated forms of these fruits, as well as among different cultivar groups. Domesticated forms have higher L:W ratios and tend to have more pointed (acute to acuminate) ends.…”

The Domestication Syndrome in Phoenix dactylifera Seeds: Toward the Identification of Wild Date Palm Populations

“…Phoenix seeds display a hard endosperm and are characterized by a deeply grooved raphe [21]. Seeds of Phoenix have been previously described [19,21,43,44]. They are of varying size and shape [19,21,43,44].…”

“…Seeds of Phoenix have been previously described [19,21,43,44]. They are of varying size and shape [19,21,43,44]. Length ranges from 7 mm in Phoenix roebelenii to 30 mm in cultivated date palm [21].…”

Evolution of sex chromosomes is prior to speciation in the dioeciousPhoenixspecies

“…According to fossils of Phoenix male flowers, dioecy could have emerged in the genus during the Eocene (~ 49.5 mya) [10, 38].…”