Island plant diversity: endangered and under-explored

This year’s International Day for Biological Diversity highlights the uniqueness of island biodiversity and the threats it faces, yet so much of island diversity remains essentially unknown.

The Palm House

On 22 May, we celebrate the International Day for Biological Diversity (IBD), an annual occasion proclaimed by the United Nations to increase understanding and awareness of biodiversity issues. This year, the focus of IBD is island biodiversity, but why? The answer is simple – islands are home to a wealth of unique and remarkable biodiversity. Islands function like natural experiments where life evolves in isolation, building up assemblages of distinct species that occur nowhere else on Earth. But this unique evolutionary history is under threat – islands are acutely sensitive to the affects of habitat destruction, invasive species and climate change. At the same time, around 600 million people live on islands, both depending and impinging upon native biodiversity. 

Why should we care about island biodiversity?

Given the intensifying pressures on island biodiversity, it is concerning that we still don’t have a clear understanding of the species diversity that occurs on many islands. This makes Kew’s work of exploring and documenting island plants all the more important. Kew has active research programmes on the plant diversity of many important island areas, such as South-East Asia, Madagascar and the Caribbean, which continue to yield previously unknown plant species at a high rate. Exciting though this may be, it leads to the inevitable and alarming conclusion that a substantial and ill-defined proportion of island plant diversity remains unknown to science. Such species may be well known to local people, but until they are 'officially' on the books, their conservation cannot be planned or their properties explored. Their extinction might even go unreported. I’ll illustrate this point with a couple of examples from my own research group – the palms.

Palms of Madagascar

Kew has been studying the palm flora of the iconic island of Madagascar since the mid-1980s. As Madagascar became more accessible around this time, Kew’s then-Head of Palm Research, John Dransfield, started the most extraordinary journey of discovery culminating in the publication, with Henk Beentje, of The Palms of Madagascar book in 1995, which documented 171 species (Dransfield & Beentje, 1995). Although this book already included 70 species and three genera that had been discovered by John and Henk, by providing critical information on Madagascar palms it also permitted the accurate identification of yet more new species. 

Since the publication of The Palms of Madagascar around 30 additional new palm species have been discovered by the Kew team (Rakotoarinivo & Dransfield, 2010), bringing the total native palm flora of the island to 199 species, all but three occurring nowhere else, and the number continues to rise. Importantly, almost all of the new species are highly threatened, as they are rare and occur in the island’s threatened humid forests, which have already been reduced to a quarter of their original extent. Mijoro Rakotoarinivo, based in Kew’s office in Antananarivo, continues to build our knowledge of the island’s palm species through targeted field research informed by sophisticated predictive modelling of palm diversity patterns. While substantial practical challenges remain, without the foundation work of John, Henk and Mijoro, the conservation of this amazing island palm flora would be out of reach.

New Guinea – the largest tropical island 

For over a decade, I have been part of a collaborative team studying the palm diversity of New Guinea, the largest tropical island in the world and one of the world’s last great botanical frontiers. Currently, we recognise an astonishing 270 palm species in New Guinea, of which 74 have been described by the project team since 1998. Most recently, with John Dransfield and the University of Papua’s Rudi Maturbongs, I described 15 new species of rattan in the journal Phytotaxa (Baker & Dransfield, 2014; Maturbongs et al., 2014). Rattans are spiny climbing palms occurring mostly in tropical Asia and are the source of rattan cane, which is the basis of a US$6.5 billion trade in cane furniture and other woven items.

In our study of the main rattan genus in New Guinea, Calamus, we made several important observations. Firstly, the prevailing taxonomy prior to our research was in a terrible mess – of the 60 or so 'species' reported, 18 were synonyms of other names and a further 12 could not be identified because essential type specimens had been destroyed in the bombing of the Berlin Herbarium in World War II. In essence, at that time, the taxonomy of this important group was non-functional. Secondly, we have found immense undocumented species diversity – by the completion of the monograph, we will have described 30 new species, some discovered by us during recent field exploration, others were found as old specimens languishing unidentified in herbaria since their collection decades earlier.

Important, widespread species new to science

Finally, while we have discovered rare, threatened species, as in Madagascar, we have also described several that are widespread and important useful plants to local people. Calamus oresbius, for example, occurs throughout highland Papua New Guinea. I first encountered it on a particularly memorable trip to Mt. Bosavi, which ended in a dramatic helicopter rescue.... but that is another story! This palm has many local names, a potential indicator of its value for local people, and it is reported to be used as a binding for construction, and for weaving basketry and decorative armbands and waistbands. The fact that such a valuable species was hitherto unknown to science is concerning because it hinders communication that might lead to its sustainable management. It is also a lost opportunity – New Guinea is home to so many species of rattan and yet contributes little to the rattan trade. By resolving the taxonomy of these rattans, we open up their economic potential, and by clarifying the economics of biodiversity we create a stronger rationale for its preservation.

The biodiversity of islands continues to surprise us, but without fully understanding what that biodiversity is, we are powerless to protect it. Fundamental biodiversity research on islands conducted by Kew and organisations like it has never been more necessary.


Baker, W.J. & Dransfield, J. (2014). New rattans from New Guinea (Calamus, Arecaceae). Phytotaxa 163: 181–215.  Available online

Dransfield, J. & Beentje, H. (1995). The Palms of Madagascar. Royal Botanic Gardens, Kew, Richmond and the International Palm Society, 475pp.

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, Richmond, 732 pp. Buy online

Maturbongs, R.A., Dransfield, J. & Baker, W.J. .(2014). Calamus kebariensis (Arecaceae)—a new montane rattan from New Guinea. Phytotaxa 163: 235–238.  Available online

Rakotoarinivo, M. & Dransfield, J. (2010). New species of Dypsis and Ravenea (Arecaceae) from Madagascar. Kew Bulletin 65: 279–303. Available online

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