Rafflesia: The largest flower on the verge of extinction

The genus Rafflesia contains the world's largest flowers and is a subject of interest for scientists and a cultural symbol in Southeast Asia. This plant is used in local medicine and attracts tourists. However, Rafflesia remains poorly studied, and its classification is a subject of debate. It also cannot be cultivated, which threatens its conservation. Most of the 42 known Rafflesia species are under serious threat of extinction, but only one species is listed by the International Union for Conservation of Nature, and 60% of species are considered critically endangered. Over 67% of Rafflesia habitats are located outside protected areas, making them even more vulnerable. In this article, we will explore the reasons for the threats to Rafflesia and how to address them.

Risks of extinction and conservation challenges

An assessment of the extinction risk for the genus Rafflesia has been conducted. Out of the 42 known species, 25 are on the brink of extinction (classified as CR, or Critically Endangered), 15 are classified as endangered, and 2 species are considered vulnerable. Rafflesia species often have highly restricted distributions, which make them particularly vulnerable to habitat destruction. The challenges associated with their propagation and seed conservation further exacerbate the situation.

In Indonesia, all Rafflesia species are protected through the Ministry of Environment and Forestry Act (2018). However, effective implementation of this law has proven to be difficult. Rafflesia receives less attention and financial support from both government and non-governmental organizations compared to animals. Many of these plants are located in remote and inaccessible areas, which poses practical difficulties for conservation efforts.

In the less-explored region of Kalimantan, poorly known Rafflesia species of uncertain taxonomic status are likely to exist. However, some of these species may have already gone extinct due to deforestation, which is a concerning prospect since they might have disappeared before even being discovered by science. In Sumatra, several Rafflesia species inhabit government-protected forests, but data on these populations are limited. Rafflesia populations on private lands, also facing high rates of deforestation, are crucial for the survival of the species. Efforts are needed to convince landowners to protect these populations, especially through community-led initiatives and ecotourism.

In the Philippines, many Rafflesia species are rare and at risk of extinction, primarily due to deforestation and habitat degradation. Deforestation is a major driver of species extinction in the country, and Rafflesia is no exception. Many Rafflesia populations are in severely degraded or regenerating forests near human settlements, making them vulnerable. The country's first attempts at ex-situ propagation for Rafflesia have been initiated, but challenges in international material movement make such efforts increasingly complex.

The overarching threat to Rafflesia is habitat loss through deforestation and habitat degradation, which reduces available space for these plants. There is a pressing need for more active research and conservation efforts for Rafflesia, including the involvement of local communities and more effective measures within countries.

Measures that have been taken so far

Southeast Asia is one of the world's richest regions in terms of plant diversity. The genus Rafflesia, with the largest solitary flower, is mainly restricted to this region, particularly in the Philippines, the islands of Borneo, Java, Sumatra, and the Malacca Peninsula. Over the past two decades, numerous new Rafflesia species have been described. In the early 21st century, the number of species doubled compared to what had been described between 1821 and 1984. Today, there are 42 known Rafflesia species, and more taxa are awaiting description. According to the theory of island biogeography, larger islands tend to host more Rafflesia species.

Since the documented discovery of Rafflesia, taxonomy within the genus has been complex and subject to changes. Type specimens are often poor or absent, and obtaining live material is often challenging. Out of the 42 known species, some have been described based on very poor specimens, sometimes even just from flower buds.

Effective conservation is hindered without a stable and objective taxonomic foundation. Complicating matters is the fact that all Rafflesia species are endoparasites, living inside their host plants, typically Tetrastigma, and they are nearly invisible for most of their life cycle. Furthermore, the Tetrastigma genus, comprising around 137 species in tropical and subtropical Asia up to the Southwest Pacific region, is taxonomically complex on its own. Indeed, identifying hosts for Rafflesia is difficult because Tetrastigma species are hard to recognize in the field, which further complicates our understanding of Rafflesia ecology.

Population genetics can also help improve conservation practices, such as protecting habitats in specific areas or identifying hidden taxa that may be missed by existing conservation strategies. However, most species are poorly understood, and the infection process of Rafflesia within the host plant remains unknown two centuries after the genus was introduced to science. Furthermore, the lack of seed banks and propagation methods makes conservation extremely challenging.

Southeast Asia has some of the fastest-disappearing forests on the planet. The highly restricted ranges of most Rafflesia species in vanishing habitats, along with the challenges associated with their propagation, demand an urgent, interregional, and unified approach to prevent the disappearance of one of the most astonishing flowers in the world. And this is what has been done:
  • Brunei is home to only one Rafflesia species, Rafflesia pricei, found within Ulu Temburong National Park. The government strictly enforces nature conservation measures, and the academic community and non-governmental organizations actively participate in efforts to conserve this rare plant and its habitat.
  • Rafflesia is considered one of Indonesia's national flowers and comprises at least 15 species. The Indonesian government is implementing conservation measures through laws and in-situ conservation campaigns, particularly in the Bogor Botanical Gardens (BBG) in West Java. Scientific research and attempts at cultivating Rafflesia in vitro are also carried out in Indonesia. However, successes in this area have been limited.
  • In Malaysia, Rafflesia has long been known and popular, serving as a significant source of income from ecotourism. There are 13 registered Rafflesia species in Malaysia, with eight of them residing in Peninsular Malaysia and five in the states of Sabah and Sarawak (Borneo). Currently, there are a few places in Malaysia where populations are managed through park administration. Additionally, in Sabah, a significant number of Rafflesia populations exist, some of which are on private lands and are carefully maintained by local landowners. These efforts in Indonesia represent just a portion of the conservation work on this species.
  • The Philippines are a center of Rafflesia diversity, with 15 species discovered, most of which have been described in the last two decades. This increase in the number of species underscores the urgent need for conservation measures for Rafflesia in the Philippines. Many populations are located in remote areas outside of protected territories and are threatened by deforestation, "slash and burn" agriculture, and other human activities. The Philippines lacks a comprehensive Rafflesia conservation strategy, with conservation efforts being partially carried out by local authorities and communities, highlighting the importance of developing a holistic conservation strategy for this genus.
  • In Thailand, only one Rafflesia species, R. kerrii, is found, and it is limited to the southern province of Surat Thani within Khao Sok National Park. This species is a symbol of the Surat Thani province and a valuable product for local communities. However, there is no coordinated effort for the conservation of this species and other Rafflesia species in Thailand.

Measures to be taken

The only consistently successful ex situ conservation propagation program for Rafflesia is located at BBG in Indonesia. Implementing the expertise of this international center of excellence at the local level will enable the establishment of local ex situ conservation collections in countries where species are most at risk.

Community conservation and devolved ownership measures are working effectively. Groups connected through social networks raise local awareness, providing protection to the locations.

Many existing populations are situated in unprotected areas and face a significant threat from habitat destruction. For instance, in the Philippines, some localities fall outside areas with protected status. However, local government authorities have declared "Critical Habitat Area" status, allowing for additional funding and the implementation of conservation measures at the local level. The most effective tool for the conservation of Rafflesia and related genera remains the protection of their habitat.