Researchers issue urgent call to save the world’s largest flower -Rafflesia - from extinction
IMAGE: A RARE GLIMPSE INTO THE INTERIOR OF RAFFLESIA ARNOLDII. IMAGE CREDIT: CHRIS THOROGOOD. view more
CREDIT: A RARE GLIMPSE INTO THE INTERIOR OF RAFFLESIA ARNOLDII. IMAGE CREDIT: CHRIS THOROGOOD.
- New study finds that most Rafflesia species, which produce the world’s largest flowers, face extinction.
- Lack of protection at local, national, and international levels means that remaining populations are under critical threat.
- Researchers propose an urgent action plan to save these remarkable flowers, building on local success stories.
An international group of scientists, including botanists at the University of Oxford’s Botanic Garden, has issued an urgent call for coordinated action to save the iconic genus Rafflesia, which contains the world’s largest flowers. This follows a new study which found that most of the 42 species are severely threatened, yet just one of these is listed in the International Union for Conservation of Nature (IUCN)’s Red List of Threatened Species. Furthermore, over two thirds (67%) of the plants’ habitats are unprotected and at risk of destruction.
Rafflesia, one of the greatest botanical enigmas, has aroused curiosity among scientists for centuries. The plant is a parasite that infects tropical vines in jungles across Southeast Asia (Brunei, Indonesia, Malaysia, the Philippines, and Thailand). For most of its lifecycle, Rafflesia is hidden from sight, existing as a system of thread-like filaments that invades its host. At unpredictable intervals, the parasite produces a cabbage-like bud that breaks through the vine’s bark and eventually forms a giant, five-lobed flower, up to a metre across. This produces a foul scent of rotting meat to attract pollinating flies, earning it the alternative name ‘corpse flower.’
With such an elusive lifecycle, Rafflesia remains poorly understood, and new species are still being recorded. To better understand the vulnerability of these unique plants, a group of scientists established the first coordinated global network to assess the threats facing Rafflesia.
The results of the study found that all 42 Rafflesia species are under threat: based on the criteria used by the IUCN, the scientists classified 25 as ‘Critically Endangered’, 15 as ‘Endangered’, and two as ‘Vulnerable’.* Furthermore, over two-thirds (67%) are unprotected by regional or national conservation strategies.
Rafflesia species often have highly restricted distributions, making them particularly vulnerable to habitat destruction. The study found that many of the remaining populations contain only a few individuals located in unprotected areas at critical risk of conversion for agriculture. Since attempts to propagate Rafflesia in botanic gardens have had limited success so far, this makes habitat conservation an urgent priority.
To address these threats, the researchers recommend that all Rafflesia species are immediately added to the IUCN Red List of Threatened Species. Currently just one is listed: Rafflesia magnifica.
The team propose a four-point action plan for governments, research centres, and conservation organisations:
- Greater protection of Rafflesia habitats, targeting populations most at risk. Habitat protection was identified as the single best tool for Rafflesia conservation. Southeast Asia has the fastest disappearing forests on the planet, and many of the known Rafflesia populations are perilously close to growing human settlements.
- Better understanding of the full diversity of Rafflesia that exists, to inform decision-making. It is thought that Rafflesia species still remain undocumented, while others have gone extinct before they were even known to science. We cannot protect what we do not know to exist, so sampling expeditions and genetic analyses are required to understand how many Rafflesia species there really are.
- Develop methods to successfully propagate Rafflesia outside their native habitat. These could include grafting Rafflesia-infected vines onto uninfected vines for species where habitat destruction is likely.
- Introduce new ecotourism initiatives to engage local communities in Rafflesia conservation. Providing funding and training for local specialist guides would be an effective way to help protect local Rafflesia populations and raise awareness of the need for conservation.
Despite the challenges, the study also highlighted valuable success stories that could offer important insights for Rafflesia conservation elsewhere. For instance:
- Bogor Botanic Garden in West Java, Indonesia, has become a centre of excellence for Rafflesia propagation, after a series of successful blooming events, including 16 for the species Rafflesia patma. Knowledge-sharing activities would help spread best practices to regions where this is needed urgently.
- In West Sumatra, groups of local villagers are benefitting from Rafflesia ecotourism by forming ‘pokdarwis’: tourism awareness groups linked to social media. Many of these announce Rafflesia blooming events on social media platforms to build awareness of populations, and to attract paying tourists while carefully managing the risks of, for example, trampling. These activities could be developed as a template to disseminate to areas where community involvement with Rafflesia conservation is scarce.
Dr Chris Thorogood, Deputy Director of the University of Oxford Botanic Garden and an author of the study said: ‘This new study highlights how the global conservation efforts geared towards plants – however iconic – have lagged behind those of animals. We urgently need a joined-up, cross-regional approach to save some of the world’s most remarkable flowers, most of which are now on the brink of being lost.’
Adriane Tobias, forester from the Philippines said: ‘Indigenous peoples are some of the best guardians of our forests, and Rafflesia conservation programmes are far more likely to be successful if they engage local communities. Rafflesia has the potential to be a new icon for conservation in the Asian tropics.’
Chris Thorogood with Rafflesia arnoldii, the largest flower in the world, in Sumatra. Image credit: Chris Thorogood.
Dang Zul, Village Leader, with Rafflesia bengkuluensis in Sumatra illustrated in pencil by Chris Thorogood.
Rafflesia bengkuluensis with its custodians in Sumatra. Image credit: Chris Thorogood.
Rafflesia bengkuluensis with its custodians in Sumatra. Image credit: Chris Thorogood.
Rafflesia kemumu in the rainforest of Sumatra. Image credit: Chris Thorogood.
Rafflesia kemumu in the rainforest of Sumatra. Image credit: Chris Thorogood.
The study ‘Most of the world’s largest flowers (genus Rafflesia) are now on the brink of extinction’ will be published in Plants, People, Planet at 00:01 BST Wednesday 20 September at https://nph.onlinelibrary.wiley.com/doi/10.1002/ppp3.10431. To view a copy of the manuscript before this, contact Dr Chris Thorogood: chris.thorogood@obg.ox.ac.uk
A series of Rafflesia images with captions to use with media articles is available at https://drive.google.com/drive/folders/1KSwZXuCMLUMbYkr999Hj0-_hizOvdogv?usp=drive_link These images may be used if the caption and credit are included.
Dr Chris Thorogood has worked for many years alongside botanists and foresters in Southeast Asia to document the huge, mysterious blooms of Rafflesia. His new book Pathless Forest tells the story of his journey to study and protect this remarkable plant – both a thrilling adventure story and an inspirational call to action to safeguard a fast-disappearing wilderness. Pathless Forest is due to be published by Penguin in April 2024.
The study involved researchers from University of Oxford Botanic Garden; Department of Biology, University of Oxford; Institute of Human Sciences, University of Oxford; University of the Philippines Los Baños; National Research and Innovation Agency of Indonesia (BRIN); Universitas Bengkulu (Indonesia); Forest Research Institute Malaysia; Synthetic Biology Indonesia; Genbinesia Foundation (Indonesia); Universitas Gadjah Mada (Indonesia).
*Definitions as provided by the International Union for Conservation of Nature (IUCN) Red List of Threatened Species:
- Critically Endangered: Critically Endangered (Cr) is the highest risk category assigned by the IUCN for wild species. Critically endangered species means a species numbers have decreased, or will decrease by 80% within three generations. It is therefore considered to be facing an extremely high risk of extinction in the wild.
- Endangered: Endangered (EN) species is a population of organisms which is at risk of becoming extinct because it is either few in numbers, or threatened by changing environmental or predation parameters. It could also mean that, due to deforestation, there may be a lack of food and/or water. It is therefore considered to be facing a very high risk of extinction in the wild.
- Vulnerable: Vulnerable (VU) species is one which has been categorised by the IUCN as likely to become endangered unless the circumstances threatening its survival and reproduction improve. It is therefore considered to be facing a high risk of extinction in the wild.
About the Oxford Botanic Garden and Arboretum
Oxford Botanic Garden is the UK’s oldest botanic garden, founded in 1621. The Garden was first established as a physic garden for the cultivation of medicinal plants, and still occupies a unique position in terms of its history and academic location to this day. It was the birthplace of botanical science in the UK and has been a centre for plant research since the 1600s.
Oxford Botanic Garden’s mission is to share the scientific wonder of plants and the importance of plants with the world. It holds a collection of about 5,000 different types of plant, together with its sister site, Harcourt Arboretum. Some of these species exist nowhere else and are of international conservation importance.
About the University of Oxford
Oxford University has been placed number 1 in the Times Higher Education World University Rankings for the seventh year running, and number 3 in the QS World Rankings 2024. At the heart of this success are the twin-pillars of our ground-breaking research and innovation and our distinctive educational offer.
Oxford is world-famous for research and teaching excellence and home to some of the most talented people from across the globe. Our work helps the lives of millions, solving real-world problems through a huge network of partnerships and collaborations. The breadth and interdisciplinary nature of our research alongside our personalised approach to teaching sparks imaginative and inventive insights and solutions.
Through its research commercialisation arm, Oxford University Innovation, Oxford is the highest university patent filer in the UK and is ranked first in the UK for university spinouts, having created more than 300 new companies since 1988. Over a third of these companies have been created in the past five years. The university is a catalyst for prosperity in Oxfordshire and the United Kingdom, contributing £15.7 billion to the UK economy in 2018/19, and supports more than 28,000 full time jobs.
JOURNAL
Plants People Planet
ARTICLE TITLE
Most of the world’s largest flowers (genus Rafflesia) are now on the brink of extinction
Contours that kill: Geometry influences prey capture in carnivorous pitcher plants
IMAGE: CAPTION: BOTANIST DR CHRIS THOROGOOD WITH PITCHER PLANTS AT OXFORD BOTANIC GARDEN. CREDIT: CHRIS THOROGOOD. view more
CREDIT: CAPTION: BOTANIST DR CHRIS THOROGOOD WITH PITCHER PLANTS AT OXFORD BOTANIC GARDEN. CREDIT: CHRIS THOROGOOD.
Researchers at the University of Oxford’s Botanic Garden and the Mathematical Institute have shown that the shape, size, and geometry of carnivorous pitcher plants determines the type of prey they trap. The results have been published today in the Proceedings of the National Academy of Sciences (PNAS).
Pitcher plants (genus Nepenthes) are a type of carnivorous plant found in the tropics, especially in Southeast Asia. Their name refers to the hollow, cup-like structures they produce to capture animal prey (typically insects). Pitcher plants come in an enormous variety of shapes and sizes from tubes to goblets, some even with spine-like ‘teeth’ – but why they differ so markedly is a mystery.
‘I first encountered these extraordinary plants in the wild in Southeast Asia nearly twenty years ago.’ recalls Dr Chris Thorogood, botanist and Deputy Director of Oxford Botanic Garden. ‘I remember wondering: how and why do they vary so much? To have helped solve this mystery is truly exciting.’
The mechanism by which pitcher plants capture prey is well known: each pitcher has a slippery rim at the top, called a peristome, covered in ridges that collect a film of water. This causes the prey to skid and fall into a pool of digestive juices at the bottom of the pitcher, similar to a car aquaplaning on water. But although this process is common to all pitcher plants, the shape of the rim ranges from simple cylinders, to highly ornate, fluted, or toothed structures. The more lavish the rim, the greater the cost to produce it: so why don’t all pitcher plants just produce a simple structure?
To address this question, the team applied mathematical models to pitcher plants grown at the Botanic Garden, to see what effect the rim’s shape has on prey capture. Shapes were classified into four groups that exist in nature and could be easily compared using mathematical reconstructions. Hypothetical capture efficiencies were measured for each shape using a ‘point mass’ – the equivalent of an insect sliding into the trap. The energetic cost of producing the rim was then calculated by examining the relative area and steepness of the different structures.
Derek Moulton, Professor of Applied Mathematics at the University of Oxford’s Mathematical Institute, explained: ‘Mathematical reconstructions enable us to explore the trade-offs that exist in these plants in nature. Large, flared rims are costly for a plant to produce. By simulating both realistic peristomes and extreme versions – geometries that don’t exist in nature – we were able to show that in an optimal structure, the cost of production might be offset by the extra prey that can be caught.’
‘A similar situation exists regarding trap size,’ added Dr Hadrien Oliveri, Postdoctoral Researcher at the University of Oxford’s Mathematical Institute. ‘We might expect the size of the rim to correlate with the prey most commonly available in a given habitat – be that ants or beetles, for example.’
To investigate the impact of the trap size, the team developed a mathematical model to link the 3D geometries of pitcher plant rims with the physical mechanics of prey capture. The model incorporated geometrical features of the rims - including width, degree of flaring, and orientation – and the stability and sliding direction of prey placed at various points.
The results suggested that variations in peristome geometries had a profound effect on what the plant could catch. For example, the geometry of highly flared peristomes appeared to be particularly suited to capturing walking insects such as ants.
Pitcher plants in nature are found in nitrogen-poor environments – such as mountain slopes, swamps and tropical forests. This means their ability to capture nitrogen from trapped insects gives them an advantage over non-carnivorous plants. Each of these habitats has a unique combination of potential prey, raising the possibility that pitcher plants evolved a variety of traps to tap into the various types of available insects in a given place.
‘Just as birds’ beaks are shaped differently to feed on nuts, seeds, or insects and so on,’ explained Dr Thorogood, ‘these pitcher plants are well-adapted to the different forms of prey that exist in their environments.’
But despite the popular appeal of these ‘green predators’, studying them in the wild can be difficult. Consequently, mathematical approaches can be a powerful way to shed light on these botanical curiosities.
‘Observing these plants in their natural environments is of course the best way to understand them. But many of these plants grow in remote, inhospitable places, so studying them in nature can be challenging’ said Dr Thorogood.
‘Working together is a powerful way for mathematicians and biologists to understand how and why such extraordinary organisms evolved, and to come up with new hypotheses,’ said Alain Goriely, Professor of Mathematical Modelling at the Mathematical Institute. ‘Mathematical modelling enables us to test them.’
The team plans to continue their work on pitcher plants, and other plants grown at the Botanic Garden – a living library for scientists to explore.
Notes for editors:
For media enquiries and interview requests contact Dr Caroline Wood: caroline.wood@admin.ox.ac.uk
Images of pitcher plants for use in articles can be accessed here: https://drive.google.com/drive/folders/12ERYe5g8DjEUNUV4euIAscJsAAkObWIo?usp=sharing
A YouTube video summary of the results can be found here: https://www.youtube.com/watch?v=gBIJwVOsPok
The study ‘Mechanics reveals the role of peristome geometry in prey capture in carnivorous pitcher plants (Nepenthes)’ has been published in PNAS: https://www.pnas.org/doi/10.1073/pnas.2306268120
About the Oxford Botanic Garden and Arboretum
Oxford Botanic Garden is the UK’s oldest botanic garden, founded in 1621. The Garden was first established as a physic garden for the cultivation of medicinal plants, and still occupies a unique position in terms of its history and academic location to this day. It was the birthplace of botanical science in the UK and has been a centre for plant research since the 1600s.
Oxford Botanic Garden’s mission is to share the scientific wonder of plants and the importance of plants with the world. It holds a collection of about 5,000 different types of plant, together with its sister site, Harcourt Arboretum. Some of these species exist nowhere else and are of international conservation importance.
About the University of Oxford
Oxford University has been placed number 1 in the Times Higher Education World University Rankings for the seventh year running, and number 2 in the QS World Rankings 2022. At the heart of this success are the twin-pillars of our ground-breaking research and innovation and our distinctive educational offer.
Oxford is world-famous for research and teaching excellence and home to some of the most talented people from across the globe. Our work helps the lives of millions, solving real-world problems through a huge network of partnerships and collaborations. The breadth and interdisciplinary nature of our research alongside our personalised approach to teaching sparks imaginative and inventive insights and solutions.
Through its research commercialisation arm, Oxford University Innovation, Oxford is the highest university patent filer in the UK and is ranked first in the UK for university spinouts, having created more than 200 new companies since 1988. Over a third of these companies have been created in the past three years. The university is a catalyst for prosperity in Oxfordshire and the United Kingdom, contributing £15.7 billion to the UK economy in 2018/19, and supports more than 28,000 full time jobs.
JOURNAL
Proceedings of the National Academy of Sciences
ARTICLE TITLE
Mechanics reveals the role of peristome geometry in prey capture in carnivorous pitcher plants (Nepenthes)
Caption: Botanist Dr Chris Thorogood with pitcher plants at Oxford Botanic Garden. Credit: Chris Thorogood.
Caption: Nepenthes pitcher plants. Credit: Chris Thorogood.
Caption: Pitcher plants growing at Oxford Botanic Garden. Credit: Chris Thorogood.
CAPTION
Caption: The deadly rim of the pitcher plant’s trap. Credit: Chris Thorogood.
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