Revisiting the Madagascan suicide palm
Kew scientist Lauren Gardiner recounts the tale of the discovery of the extraordinary Madagascan suicide palm, Tahina spectabilis.
An unexpected discovery
It is not hyperbole to describe Tahina spectabilis as a truly extraordinary plant. The palm was only discovered and brought to our attention a decade ago, in 2006, by Xavier Metz, the manager of a cashew plantation. Xavier’s plantation is on a remote peninsula in northwest Madagascar near a village called Antanamarina. While out walking, Xavier and his family found an enormous palm with leaves up to 5m across, growing in an outcrop of limestone karst (called tsingy in Madagascar). The tsingy ‘island’, called Antsingilava was surrounded by grassland grazed by zebu (the local Madagascan cattle) with a rice field on one side.
Returning a year later, the family discovered that one of the trunked individuals was flowering – producing a massive pyramidal inflorescence bearing millions of tiny flowers. Tahina is hapaxanthic, a life strategy that means that it flowers and sets seed just once, in one enormous flowering event, before the plant dies.
Kew’s involvement in Tahina from the start
Photographs of the flowering individual were posted online in early December 2006 as Xavier tried to track down someone who could name the palm he had found. Within 24 hours, news of the images had reached Kew, and the attention of John Dransfield, Kew’s then Head of Palm Research. Now retired, but still a very active Honorary Research Fellow at Kew, John immediately knew that this palm was special. The mystery palm did not match any other known Madagascan species, nor did it match anything found on continental Africa. Morphological, anatomical, and molecular studies all showed that the new discovery belonged in the subfamily Coryphoideae, in the Chuniophoeniceae tribe, with its nearest relatives being Chuniophoenix from China and Vietnam, Kerriodoxafrom Thailand, and Nannorrhops from Arabia, Afghanistan, and Pakistan. This extreme biogeographically isolated distribution with its closest relatives, and genetic distance from all other Madagascan palms, makes the already visually striking palm extremely significant.
John and colleagues published the new genus, and monotypic species within it, in 2008 (Dransfield et al. 2008a, 2008b) and managed to get the genus into the manuscript of the second edition of Genera Palmarum (Dransfield et al. 2008c) just before it went to the printers.
Mijoro Rakotoarinivo, then the palm specialist in the Kew Madagascar team in Antananarivo (and now a lecturer at the University of Antananarivo), visited the Tahina site in January 2007 to take measurements and collect herbarium specimens – duplicate specimens were sent to Kew, and can now be found in the Kew’s herbarium. Mijoro also engaged in discussions with the local people and representatives of the cashew plantation (VERAMA, part of the UNIMA group) near the site on how to protect Tahina in the future.
The new species was published in 2008, and this Kew Science story caught the imagination and interest of news outlets worldwide – international newspapers dubbed Tahina ‘Kew’s Madagascan suicide palm’ on the basis of its hapaxanthic life history causing the palm to ‘flower itself to death’.
Mijoro returned to Antsingilava the following year with Alison Shapcott, a long-term collaborator with Kew, and Associate Professor at the University of the Sunshine Coast, Australia. A specialist in population genetics, Alison carried out a demographic survey of the population and collected DNA samples from the plants, to study in her laboratory in Australia.
Microsatellite work undertaken by Alison and one of her students, Heather James, showed that the genetic diversity of the individuals at the site was extremely low (James 2010). There were signs, however, that other populations of Tahina may exist, as some rare alleles not found in the main tsingy population were found in individuals growing at the edge of the tsingy and in one of the two isolated individuals found 0.2km and 2.25km away.
Seed sales for community-based conservation
Kew’s Millennium Seed Bank and local partner Silo National des Graines Forestières worked with VERAMA and the local community at Antanamarina to sell seeds collected in 2007. These seeds were snapped up by the horticultural community worldwide, and, combined with high germination rates and the exchange of seed and seedlings between Kew and other botanic gardens, this species is now found growing in many public and private gardens around the world.
Funds from the sale of the seeds went back to the local community and were used to build a new school and pump for the village well, as well as the creation of a firebreak around the vulnerable tsingy, surrounded as it is in a sea of inflammable grassland.
From a conservation perspective, Tahina is now represented in multiple ex situ collections which is significant, but it should be noted that the seeds for these plants came from a single flowering event, and are known to represent low genetic diversity.
Kew researchers had not been back to Antsingilava, until September this year. The next entry in the Kew Science blog will describe the journey back to the only known location of this palm, what the team of scientists found there and the implications for the future of this species.
References
Dransfield, J., Rakotoarinivo, M., Baker, W. J., Bayton, R. P., Fisher, J. B., Horn, J.W., Leroy, B. & Metz, X. (2008a). A new Coryphoid palm genus from Madagascar. Botanical Journal of the Linnean Society 156: 79–91.
Dransfield, J., Leroy, B., Metz, X. & Rakotoarinivo, M. (2008b). Tahina: a new palm genus from Madagascar. Palms 52: 31-39. Available online
Dransfield, J., Uhl, N. W., Asmussen, C. B., Baker, W. J., Harley, M. M. & Lewis, C. E. (2008). Genera Palmarum – the evolution and classification of palms. Royal Botanic Gardens, Kew. 732 pages. Buy online from Kew books
James, H. J. (2010). Conservation genetics of Tahina spectabilis, newly discovered palm from Madagascar. Honours Thesis, University of the Sunshine Coast, Queensland, Australia.