Rafflesia (Rafflesia spp)

by Fletcher & Baylis

Facts

Kingdom Plantae
Phylum Tracheophyta
Class Magnoliopsida
Order Proteaceae
Family Rafflesiaceae
Genus Rafflesia (1)

Size Flower diameter: up to 91 cm (2)

Rafflesia manillana is classified as Endangered on the 1997 IUCN Red List of Threatened Plants (1). R. keithii and R. pricei are classified as Vulnerable; R. cantleyi, R. kerrii and R. zollingeriana are classified as Rare (1); R. hasseltii is classified as Indeterminate (1).

Medium Rafflesia-kethii flower in the rainforest

The dramatic Rafflesia flowers are the largest single flowers in the world; the leathery petals can reach over 90 centimetres across (2). Rafflesia is a parasite that depends completely upon its host; the majority of the plant's tissues exist as thread-like strands entirely within the host's cells (3). These host plants are vines of Tetrastigma spp., and the Rafflesia plant is itself not visible until the reproduction stage when flowers first bud through the woody vine and then open into the magnificent spectacle that is world-renowned today (4). The flowers can take up to 10 months to develop from the first visible bud to the open bloom, which may last no more than a few days (5). Currently 17 species of Rafflesia are recognised and these mainly differ in the morphology of their flowers (4). In general however, the flowers consist of 5 leathery petals that are orange in colour and mottled with cream-coloured warts (2). There is a deep well in the centre of the flower containing a central raised disc raised that supports many vertical spines (2). The sexual organs are located beneath the rim of the disk, and male and female flowers are separate (2).

Species of Rafflesia are known from peninsular Malaysia, Sumatra, Java, southern Thailand, Borneo and southern Philippines (4). The genus as a whole is considered to be rare although information on distribution is lacking due to the difficulties of identifying plants within their host vines (4).

Rafflesia plants are specialist parasites only found in association with specific species of the host vine Tetrastigma spp. These vines are found in both primary and secondary rainforest (4).

The enormous Rafflesia flowers are believed to be pollinated by flies; alighting on the central disk flies crawl underneath it where they come into contact with the sexual organs (2). It has been reported that the flowers have a strong smell of rotting flesh but it is unclear whether this acts to attract flies or is merely a by-product of the decaying petals, which reduce into a black slimy mess after around 4 days (2).

Rafflesia are inherently rare as a result of a number of factors of their life cycle; they have a double habitat specialisation, as they can only successfully parasitise particular species and these species in turn are found only in specific habitats (4). In addition to this factor, there is an extremely unbalanced sex ratio in the Rafflesia flowers observed, with many more male than female flowers (4). Flower buds have a high level of mortality and only 10-18% go on to bloom, these only lasting for a few days; the chances of a male and female flower being in bloom at the same time in a close enough vicinity to be pollinated is therefore extremely slim (4). In addition to these inherent factors, there is widespread habitat destruction within much of the rainforested area of Southeast Asia and Rafflesia buds are also collected for traditional medicine, to treat fertility problems, in parts of their range (5).

Rafflesia species are protected in a number of reserves within their range such as Mount Kinabalu National Park in Sabah on the island of Borneo (5). Habitat protection is one of the key factors in securing the future of this species and this magnificent flower is a huge draw to tourists, bringing much needed revenue to the area. More investigation into the life cycle of this unusual species is urgently needed to enable propagation and ex-situ conservation measures (3). Recent success in propagating R. keithii is an encouraging step forward in the preservation for future generations of one of the world's most astonishing plant species (4).

Nais, J. (2001) Rafflesia of the World. Sabah Parks, Kota Kinabalu, Sabah.

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Ex-situ: Measures to conserve a species or habitat that occurs outside of the natural range of the species, e.g. in zoos or botanical gardens.

Genus: A category used in taxonomy, which is below ‘family' and above ‘species'. A genus tends to contain species that have characteristics in common. The genus forms the first part of a ‘binomial' Latin species name; the second part is the specific name.

Parasite: Vb. parasitise: an organism that derives its food from, and lives in or on, another living organism at the host's expense.

References
Walter, K.S. and Gillett, H.J. (1998) 1997 IUCN Red List of Threatened Plants. IUCN – The World Conservation Union, Gland, Switzerland and Cambridge, UK.

Attenborough, D. (1995) The Private Life of Plants. BBC Books, London.

Western Michigan University (March, 2003)
http://unix.cc.wmich.edu/~tbarkman/rafflesia/Rafflesia.html

Nais, J. (2001) Rafflesia of the World. Sabah Parks, Kota Kinabalu, Sabah.

Wild Borneo Net (March, 2003)
http://wildborneo.virtualave.net/index.html