Carpological Analysis of Phoenix (Arecaceae): Contributions to the Taxonomy and Evolutionary History of the Genus
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bs_bs_banner Botanical Journal of the Linnean Society, 2014, 175, 74–122. With 25 figures Carpological analysis of Phoenix (Arecaceae): contributions to the taxonomy and evolutionary history of the genus DIEGO RIVERA FLS1*, CONCEPCIÓN OBÓN FLS2, JOAQUÍN GARCÍA-ARTEAGA2, TERESA EGEA2, FRANCISCO ALCARAZ1, EMILIO LAGUNA3, ENCARNA CARREÑO1, DENNIS JOHNSON4, ROBERT KRUEGER5, JOSÉ DELGADILLO6 and SEGUNDO RÍOS7 1Depto. Biología Vegetal, Fac. Biología, Universidad de Murcia, 30100 Murcia, Spain 2Depto. De Biología Aplicada, Escuela Politécnica Superior de Orihuela. Ctra. Beniel, Km 3,2. Universidad Miguel Hernández, 03312 Orihuela, Alicante, Spain 3Generalitat Valenciana. Conselleria d’Infraestructures, Territori i Medi Ambient. Servei de Vida Silvestre/Centre per a la Investigació i Experimentació Forestal. Avda. Comarques del País Valencià, 114. 46930 Quart de Poblet. València, Spain 43726 Middlebrook Ave, Cincinnati, OH 45208, USA 5National Clonal Germplasm Repository for Citrus and Dates, Riverside, 1060 Martin Luther King Blvd, Riverside, CA 92507-5437, USA 6Facultad de Ciencias, Campus de Ensenada, Universidad de Baja California, Ensenada, Baja California ZP 22830, Mexico 7CIBIO, Universidad de Alicante, Alicante, Spain Received 23 July 2013; revised 17 November 2013; accepted for publication 23 February 2014 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 archaeobo- tanical 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 *Corresponding author. E-mail: [email protected] 74 © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175, 74–122 CARPOLOGICAL ANALYSIS OF PHOENIX 75 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. ADDITIONAL KEYWORDS: Holocene – Miocene – multivariate analysis – palaeobotany – Palaeotropical – Phoenicites – Pleistocene – seed morphology – Tertiary. INTRODUCTION the cultivated gene pool, the status of P. atlantica A.Chev. as distinct from P. dactylifera and its possible The genus Phoenix L. (Arecaceae) comprises 13 presence on the African continent (Mauritania and (Barrow, 1998) to 20 (Beccari, 1890) species of mostly Morocco) need to be clarified (Pintaud et al., 2013). tropical, dioecious palms with solitary stems, rarely Fruits (dates) normally develop after pollination, branched, or, in some species, with a short under- resulting in dates with seeds. Unpollinated female ground stem, ending in a crown of 20–150 pinnate flowers may develop seedless, poor-quality fruits that leaves. The fruits are berries (with a fleshy mesocarp are normal in other respects. Date fruits are ellipsoi- and a membranous rudimentary endocarp), known as dal to ovoid or almost cylindrical. Dimensions of dates ‘dates’, borne in clusters of tens or hundreds, which are variable, ranging from 10×5mminP. roebelenii develop from three-carpellate female flowers, in O’Brien (Iossi, Vitti & Rubens, 2006), to 75 × 35 mm which two carpels normally abort. in P. dactylifera ‘Medjool’. The phylogenetic isolation of Phoenix has long been Phoenix seeds are typically elliptical and slightly established. It has been placed in tribe Phoeniceae flattened dorsiventrally and have a longitudinal (Uhl & Dransfield, 1987; Asmussen et al., 2006) in furrow on the ventral face. On the dorsal face, the subfamily Coryphoideae, appearing to be the only operculum or micropyle appears at the middle point of palm group displaying the induplicate insertion of the seed, although, often, it can be slightly displaced leaf segments (Uhl et al., 1995; Dransfield et al., towards the proximal or distal end. Only one species, 2005). Phoenix differs from related genera of Coryph- P. paludosa Roxb., has a nearly basal operculum. The oideae by having pinnate rather than palmate leaves. rigid date seeds (because of the hard endosperm) are Although firmly anchored in Coryphoideae, Phoenix erroneously called date ‘stones’ or ‘kernels’ in the appears to be on a deep branch in phylogenetic trees, archaeobotanical literature, leading the reader to being sister to the large, pantropical tribe Trachy- misinterpret dates as drupes (Hopf, 1983; Kislev, carpeae (Dransfield et al., 2008). Molecular phyloge- Hartmann & Galili, 2004). Problems during pollina- netic dating placed the divergence of the Phoeniceae tion and fruit development can lead to the incom- lineage during the early Tertiary (Couvreur, Forest & pletely developed or abnormal seeds. Baker, 2011). Date fruits and their seeds present a set of charac- Phoenix dactylifera L. (the date palm) has the ters that are used as descriptors for the systematics of widest distribution and the highest morphological Phoenix spp. and cultivars (Beccari, 1890; Barrow, diversity in Phoenix, and it is the most numerous in 1998; IPGRI, 2005). However, some of these charac- terms of individuals and populations. Although ters, such as testa colour, endosperm colour or the hybrid origins have been proposed, molecular data presence/absence of a ruminate endosperm, cannot be have demonstrated that P. dactylifera is a true used for identification of palaeobotanical materials, species, distinct from all other species of the genus because they are lost during pre- and post-depositional (Pintaud et al., 2010). Recent genetic data and phylo- processes affecting the seeds. However, seed morphol- genetic data based on DNA sequences of the plastid ogy is taxonomically relevant and several nomenclatu- loci psbZ–trnfM and rpl16–rps3 indicate a strong ral types of Phoenix spp. are seeds or seed illustrations, geographical structure of the genetic diversity of the for example, P. pusilla Gaertn. (Gaertner, 1788–1791). date palm at all scales (local, regional, global) and the The shape of Phoenix seeds is characteristic and allows importance of isolation and intraspecific gene flow in determination of both fossil and archaeobotanical (car- shaping the present day agrobiodiversity. Although bonized, desiccated or mineralized) materials at the there is no evidence of interspecific hybridization in generic level. However, in routine identifications of © 2014 The Linnean Society of London, Botanical Journal of the Linnean Society, 2014, 175, 74–122 76 D. RIVERA ET