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Phylogenetics and Conservation of Madagascan Euphorbia (Euphorbiaceae)

Euphorbia sp. Photo: P. Hoffmann.

This PhD study by Thomas Haevermans was a collaboration led by the Museum National d’Histoire Naturelle, Paris, and co-supervised at the Kew Herbarium. It defined the main Malagasy species groups of Euphorbia, one of the largest plant genera on earth, and placed them in a global context according to other recent phylogenetic studies in the genus. Euphorbia (as understood today) is characterized by the possession of a cyathium (a cup-like inflorescence structure), but beyond that, the genus is a patchwork of hyperspecialized plants in which homology assessment of morphological structures is very problematic, making a global morphological cladistic analysis unrealistic. The molecular phylogenetic analysis was carried out at the Jodrell Laboratory while on a SYNTHESYS grant. As a result of the ITS sequence analysis, clades endemic to Madagascar were identified and their internal relationships evaluated. This allowed a partial taxonomic revision as well as a consistent morphological cladistic analysis of well circumscribed clades. This work is still ongoing in Paris: resolution and support at basal nodes are still not satisfactory, and relationships of individual species within the clades still need further clarification. In the future, it is intended to study other DNA regions to resolve the remaining nodes and to eventually build a sound classification of the genus. This goal, however, can only be achieved in an international collaboration. The project involved extensive fieldwork in Madagascar and resulted in a successful PhD for Thomas Haevermans and several collaborative papers.

Part of this study was the evaluation of threat to these mainly succulent plants. They are of great horticultural value and often illegally exported. Conservation assessments of 152 taxa (including all species and infraspecific taxa of Euphorbia in Madagascar) were carried out at the Kew GIS unit. They are now published in the IUCN Red List (available at: www.redlist.org).

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