Malpighiales: key achievements 2006 - 2011

Work of the Malpighiales Team has focused on a range of projects treating diversity within Malpighiales, a large, relatively newly recognised and as yet poorly understood order. Studies ranged from taxonomic and developmental/morphological to population genetics.

Outcomes delivered over the last five years include significant publications in three main areas: evolutionary-developmental (evo-devo) work within Euphorbiaceae, gene flow studies in Populus, and phylogenetic/systematic work within Phyllanthaceae and Salicaceae. A considerable body of work has provided a strong basis for future publications or has been of a support or curatorial nature. The team adds about 1500 new accessions to the Herbarium collections each year.

The evo-devo work contributes to a better understanding of relationships among genera of Euphorbiaceae, one of the largest eudicot families, by exploring the genetic background for formation of the cyathium, a highly derived structure in the family. Detailed data on comparative floral and inflorescence morphology are the foundation for understanding reproductive structures in an ecological context, including the pollinating agents and reproductive system. Regular publications have treated the following topics: useful marker genes for the flower-inflorescence boundary, the development and homologies of perianth and floral nectaries, the key role of morphology in modelling inflorescence architecture, the homologies of the angiosperm stamen fascicle, and comparative ontogeny of the cyathium in Euphorbia and its allies (exploring the organ-flower-inflorescence boundary). Encompassed in the ongoing project Evolution of flowers and inflorescences of Euphorbiaceae the research has been presented at six conferences.

The project Genomic isolation and transcriptomic differentiation in Populus addressed the genetics of barriers to gene flow between P. alba and P. tremula, two widespread species in a tree genus of immense ecological and economic importance. Population genome scans and admixture mapping genome scans sought to identify mechanisms involved in adaptation, reproductive isolation and speciation; evolutionary trajectories of hybrid lineages and strategies for admixture mapping in hybrid zones between highly divergent populations were developed. The project has published a significant body of collaborative papers and the work presented at an average of four conferences/workshops per year, including the 2010 Ecological & Evolutionary Genomics of Adaptation Symposium, organized by the project team.

Phylogenetic/systematic publications resolving difficult plant taxa have focused on two groups : Phyllanthaceae and the salicaceous genera Salix and Populus. Phyllanthaceae, recently separated from Euphorbiaceae, is a widespread pantropical family of 60 genera and over 1700 species. Key work in the group has included three RBG Kew supervised PhDs: a phylogenetic classification of Phyllanthaceae, systematics and biogeography of Phyllanthus of Madagascar, a phylogenetic classification of tribe Poranthereae, and revisions of several other genera within the family. Salix and Populus are two widespread temperate genera with great economic importance but notoriously difficult taxonomy. A significant publication in the review period has been Willows of Ural: Atlas and Identification Key (in English and Russian). Also published by the Team are accounts for the Flora of China (Euphorbiaceae s.l., Salicaceae & Achariaceae (as Flacourtiaceae)) and treatments of Salicaceae and Achariaceae for three South American catalogues.

The Team’s World Classification and Phylogeny of Salix & Populus project will provide the first stable phylogeny for Salix and Populus, World Checklists for both genera, and a 250-character species database. In the period 2006–11, 150 Eurasian species have been treated for the database, involving field studies and examination of collections from 20 herbaria. Molecular analysis of the group, including the development of new techniques, has treated 352 taxa and produced over 1000 DNA sequences. For the World Checklist complex nomenclature has been clarified and stabilized for all Eurasian species of Salix and Populus (= 30% of all species), and 5000 names have been standardized, this critical work also upgrading the IPNI database. The research has been presented at conferences in St Petersburg and Moscow.

Traditionally including only the largely north-temperate genera Salix and Populus, Salicaceae now includes over 50 tropical genera, mostly transferred from Flacourtiaceae. The dramatic taxonomic changes, published by the Team in 2002, continue to be controversial and involve also a second family, Achariaceae. Clarification of the changes is urgently needed to halt ongoing confusion and error in Flora accounts and critical diversity assessments, at family, genus and species level. To that end, The Malpighiales Team project Taxonomic tools for Salicaceae and Achariaceae is working towards a published clarification of the changes, and treatments for the World Checklist. In 2006–2011, study has included molecular analysis, preparation of family accounts for the internationally recognized benchmark reference series Families and Genera of Vascular Plants and initial work for the Checklist.Publication of FGVP is scheduled for 2012-4.

Within the Systematic Phytochemistry and Sustainable Use Studies in Malpighiales project the results of surveys of polyhydroxyalkaloids and flavonoids from Euphorbiaceae and Passiflora, respectively, will be published in context of the most recent phylogenetic analyses for these taxonomic groups. Herbarium material of 57 species of Euphorbiaceae have been analysed for polyhydroxyalkaloids, leading to their identification in 14 species covering 11 genera. Material from 120 living collection samples and 50 herbarium samples of Passiflora have been analysed by LC-MS for flavonoids (in particular flavone C-glycosides) using liquid chromatography-mass spectrometry. This survey employed an improved method for the analysis of flavones C-glycosides by liquid chromatography-mass spectrometry developed as part of this study and published in 2006.

The Malpighiales Pollen Evolution project is relatively new and already has a paper in press. Research will provide comparative data to elucidate relationships and character evolution within the order; pollen and tapetum characters are known to be of systematic significance in other angiosperm clades. Initial work focused on the parietal clade, including an MSc project collaborative with RBG Edinburgh, and also on evolutionary stasis in Euphorbiaceae pollen in collaboration with the Muséum national d’Histoire naturelle. Work on the latter was presented at the Linnean Society Palynology Specialist Group Symposium (London, 2008) and the Bentham-Moxon Symposium (Kew, 2011). The next phase of the project, evaluating the clusoid clade, is underway.

The Wood anatomy of Malpighiales constitutes a long-term survey of significance and distribution of a wide variety of wood characteristics in the order, plotted against recent molecular cladograms at different taxonomic levels. Malpighiales includes a number of important timber taxa, Chrysobalanaceae, Clusiaceae, Euphorbiaceae, Achariaceae and Salicaceae.

Much of the Team’s work has been internationally collaborative, with partners in Europe, Russia, Canada and the USA, Brazil, China, Vietnam and Madagascar. Funding has included core funds, grants and sponsorships.

Euphorbiaceae s.l. specialism within the team has contributed strongly to RBG Kew’s Asian and African regional team checklist projects, including those for proposed conservation areas (e.g. Mefou National Park, Cameroun). A recent project has developed the Team’s web-based identification tool, an Interactive Key to Genera of Euphorbiaceae s.l., Salicaceae s.l. and Achariaceae, with over 5000 associated images created largely from RBG Kew’s herbarium collections and an online Malpighiales Scratchpad. The Scratchpad invites collaboration and includes a Malpighiales forum.

The Teams’ work is almost entirely confined to Breathing Planet Programme strategy 1.

Conferences and workshops

Members of the Malpighiales Team have presented their work at a wide range of international conferences and workshops throughout the review period (no conferences devoted specifically to Malpighiales have been held). Key examples include:

2^nd Evo-Devo conference, Ghent, Belgium, 2008. Evolution of flowers and inflorescences in Euphorbiaceae.
Linnean Society Palynology Specialist Group Symposium, London, 2008. Malpighiales Pollen Evolution.
Ecological & Evolutionary Genomics of Adaptation, 2010, Fribourg, Switzerland. Genomic isolation and transcriptomic differentiation in Populus.
Dendrology at the beginning of the XXI century, Scientific Conference in Commemoration of E. L. Wolf, 2010, St. Petersburg, Russia. World Classification and Phylogeny of Salix & Populus.

International Policies

The projects of the Malpighiales Team contribute strongly to GSPC target 1, which is especially important for this large, relatively newly described and as yet poorly understood order.

Acting Science Team Leader: Sue Zmarzty