The continued importance of the Arecaceae to mankind is in no doubt; neither is the fascination that palms hold to researchers, due in no small part to the distinct and often striking forms seen in the family. This issue provides a snapshot of recent and ongoing research directions and reinforces the conviction within the worldwide community that new generations of scientists will continue to be drawn to the challenge of palm biology in the years to come.
A family portrait: unravelling the complexities of palms by James W. Tregear, Alain Rival, and Jean-Christophe Pintaud.
Geographical ecology of the palms (Arecaceae): determinants of diversity and distributions across spatial scales by Wolf L. Eiserhardt, Jens-Christian Svenning, W. Daniel Kissling, and Henrik Balslev.
Palms (Arecaceae) are an important element of tropical vegetation across the world and serve as a model system in geographical ecology.Eiserhardt et al. review how the abiotic environment, biotic interactions and dispersal influence palm distribution and diversity patterns across spatial scales, and discuss contemporary vs. historical impacts of these factors and the scale at which they function. A key finding is that determinants of palm distributions, composition and richness vary with spatial scale.
Phylogenetic relationships among arecoid palms (Arecaceae: Arecoideae) by William J. Baker, Maria V. Norup, James J. Clarkson, Thomas L. P. Couvreur, John L. Dowe, Carl E. Lewis, Jean-Christophe Pintaud, Vincent Savolainen, Tomas Wilmot, and Mark W. Chase.
The Arecoideae is the largest, most diverse and most economically important palm subfamily and yet relationships within the group are poorly understood. Baker et al. collect nuclear DNA sequence data for the low-copy nuclear genes PRK and RPB2 from 190 palm species, covering 103 genera of Arecoideae, and generate the most extensive arecoid phylogeny published to date. Their findings strongly support the current classification of palms, resolve several well-supported ‘deep’ relationships and identify priorities for future research.
Phylogenetic utility of the nuclear genes AGAMOUS 1 and PHYTOCHROME B in palms (Arecaceae): an example within Bactridinae by Bertha Ludeña, Nathalie Chabrillange, Frédérique Aberlenc-Bertossi, Hélène Adam, James W. Tregear, and Jean-Christophe Pintaud.
Molecular phylogenetic studies of palms (Arecaceae) have not yet provided a fully resolved phylogeny of the family. Ludeña et al. test the value of AGAMOUS 1 and PHYTOCHROME B genes as new nuclear markers to improve phylogenetic resolution in the family, using the subtribe Bactridinae as a case study. The results provide new insights into the intergeneric relationships within Bactridinae and the intrageneric structure of Astrocaryum, and the existence of a monophyletic group sister to Astrocayum, corresponding to the debated genus Hexopetion, is supported. The new markers thus provide additional phylogenetic information within the palm family, and should prove useful in combination with other genes to improve the resolution of palm phylogenies.
DNA barcoding: a new tool for palm taxonomists? by Marc L. Jeanson, Jean-Noël Labat, and Damon P. Little.
Although taxonomy of palms (Arecaceae) is fairly well known, many problems remain and this is, in part, due to the difficultly of representing palm diversity with herbarium specimens. For the first time in Arecaceae, Jeanson et al. test the ultility of DNA barcoding, examining 40 out of the 48 species of the south-east Asian tribe Caryoteae (subfamily Coryphoideae). The results show 92 % species’ discrimination, which is a high rate for a barcoding experiment. They find that the two recommended ‘core’ markers, rbcL and matK, have a low discrimination rate and need to be supplemented by another marker, with nrITS2 being the preferred choice for Caryoteae.
Epigenetic imbalance and the floral developmental abnormality of the in vitro-regenerated oil palm Elaeis guineensis by Estelle Jaligot, Sophie Adler, Émilie Debladis, Thierry Beulé, Frédérique Richaud, Pascal Ilbert, E. Jean Finnegan, and Alain Rival.
The mantled somaclonal variation of oil palm (Elaeis guineensis) hampers oil production as the supernumerary female organs are either sterile or produce fruits with poor oil yields. Jaligot et al. provide an overview of research focusing on this intriguing floral phenotype, which also provides a unique opportunity to investigate epigenetic regulation of reproductive development in palms. They propose that future efforts should concentrate on epigenetic regulation targeting MADS-box genes and transposable elements, since both types of sequences are most likely to be involved in this variant phenotype.
A temporary immersion system improves in vitro regeneration of peach palm through secondary somatic embryogenesis by D. A. Steinmacher, M. P. Guerra, K. Saare-Surminski, and R. Lieberei.
Secondary somatic embryogenesis has been postulated to occur during induction of peach palm (Bactris gasipaes) somatic embryogenesis. Steinmacher et al. study this morphogenetic pathway and use zygotic embryos as explants to develop a technique for the establishment of cycling cultures using a temporary immersion system (TIS). They confirm the occurrence of secondary somatic embryos in peach palm and describe a feasible protocol for regeneration in vitro. Plantlets are obtained and after 3 months in culture their growth is significantly better in TIS than on solid culture medium.
The shoot apical meristem of oil palm (Elaeis guineensis; Arecaceae): developmental progression and dynamics by Stefan Jouannic, Marc Lartaud, Jonathan Hervé, Myriam Collin, Yves Orieux, Jean-Luc Verdeil, and James W. Tregear.
Oil palm (Elaeis guineensis) is an unbranched palm, possessing a single shoot apical meristem (SAM) that may remain active for more than 100 years. Through histological analysis and 3-D reconstructions, Jouannic et al. detail the SAM structural variations that occur during the oil palm life cycle, and find that development of the SAM is characterized by a juvenile-to-mature phase transition accompanied by establishment of a zonal pattern and modified shape. SAM zonation is dynamic during the plastochron period and displays distinct features compared with other monocots.
Pericarp development and fruit structure in borassoid palms (Arecaceae–Coryphoideae–Borasseae) by Mikhail S. Romanov, Alexey V. F. Ch. Bobrov, D. Siril A. Wijesundara, and Ekaterina S. Romanova.
The Borasseae form a highly supported monophyletic clade in the Arecaceae–Coryphoideae, and the large fruits of borassoid palms contain massive pyrenes, which develop from the middle zone of the mesocarp. Romanov et al. study pericarp anatomy during development in all eight Borasseae genera and find that the multilayered pyrene develops in the middle zone of the mesocarp, and that the growing seed dramatically compresses the inner parenchymatous zone of the mesocarp. The pericarp anatomical structure and mode of its development differ significantly from fruits of other Coryphoideae.
Twenty-five years of progress in understanding pollination mechanisms in palms (Arecaceae) by Anders S. Barfod, Melanie Hagen, and Finn Borchsenius.
Understanding of palm–pollinator interactions has implications for tropical silviculture, as well as for our knowledge of the evolution and diversification of Arecaceae. Barfod et al. review 25 years of progress in palm pollination ecology and note that more than 60 studies have been published in this period that provide new insights on autecological, comparative and synecological aspects of palm pollination. However, with detailed studies of only 3 % of all palm species and a strong geographical bias towards the South American region and a taxonomic bias towards the tribe Cocoseae, caution should be exercised when making generalizations across the family.
Ontogeny and structure of the acervulate partial inflorescence in Hyophorbe lagenicaulis (Arecaceae; Arecoideae) by N. Ortega-Chávez and F. W. Stauffer.
The palm tribe Chamaedoreeae displays flowers arranged in a complex partial inflorescence called an acervulus. Ortega-Chávez and Stauffer examine ontogeny in Hyophorbe lagenicaulis and show that the acervulus and the inflorescence rachilla form a condensed and cymose branching system resembling a coenosome. Syndesmy results from a combined process of rapid development and adnation, without or with reduced axis elongation. A study of the ten taxa of the Chamaedoreeae show that a more general definition of the type of partial inflorescence observed within the large subfamily Arecoideae would correspond to a cyme rather than to a floral triad.
Environmental regulation of sex determination in oil palm: current knowledge and insights from other species by Hélène Adam, Myriam Collin, Frédérique Richaud, Thierry Beulé, David Cros, Alphonse Omoré, Leifi Nodichao, Bruno Nouy, and James W. Tregear.
In the African oil palm, Elaeis guineensis, male and female inflorescences are produced separately in an alternating cycle that is influenced by the environment: stress conditions promote male flowering, but the underlying mechanisms of this process are unknown. Adam et al. review current knowledge of sex differentiation in oil palm together with perspectives gained from other species, and suggest that at least four different types of factor can be identified that might participate in sex determination and differentiation: abiotic factors (e.g. water stress), metabolic factors (e.g. carbon reserves), hormone status and genetic factors. They present a basic framework as a step towards understanding the interactions between the various parameters of importance in oil palm sex determination.
The anatomy of palms (Arecaceae–Palmae) review by James Tregear.
The book of palms review by James Tregear.