Tuesday, 2 November 2010

Rafflesia arnoldii

Image showing R.arnoldii with flower and bud
Rafflesia arnoldii with
flower and bud
Kingdom: Plantae
Phylum: Magnoliophyta
Class: Magnoliopsida
Order: Malpighiales
Family: Rafflesiaceae
Genus: Rafflesia
Species: Rafflesia arnoldii
Conservation Status: Not yet assessed, their numbers are most probably declining due to habitat loss
Common Name(s): Patma raksasa (local name), Corpse flower

Instead of posting about another strange animal, today I decided to post about a weird plant that is scientifically known as Rafflesia arnoldii.

Rafflesia arnoldii is a parasitic plant that holds the world record for producing the largest individual flowers. It belongs to the Rafflesia genus, and can be found in the rainforests of Bengkulu, Sumatra Island, Indonesia, and Malaysia. Flowers have been sighted in heights of up to 1,000 m (3280 feet).

The plant is also known for its hideous odor, which is reminiscent of the smell of decomposing flesh. This why it is commonly known as the "corpse flower".

Some may argue that other plants like the titan arum (Amorphophallus titanum) produce larger flowers than R. arnoldii does. However, this is a mistake, as those are actually clusters of many small flowers (inflorescence) and not individual flowers.

Image showing the flower of titan arum
Titan Arum flower

R.arnoldii lives as a parasite on the Tetrastigma vine.The plant has no leaves, stems or roots. The species grows as thread-like strands of tissue (similar to fungi), which stay in close contact with the surrounding host cells.

Despite being a plant, R.arnoldii doesn't produce chlorophyll and solely depends on the host for its survival, which provides water and all the nutrients needed for development. The plant is virtually invisible and can only be seen during the flowering stage, when the flower buds begin to develop.

As mentioned before, the species is known for producing the largest individual flowers. They have a diameter of about 1 meter (3.2 ft) and an average weight of 11 kg (24.25 pounds). They have a corpse-decaying odor and this is why R.arnoldii is commonly referred to as the "corpse flower". The odor attracts flies, beetles and other insects that pollinate the flower.

The flower buds form on the outside of the host's root or stem, taking them up to a year to flower. First,  a tiny bud appears. Gradually, this small bud develops to a cabbage-like head that eventually opens to reveal the flower. The opening process takes about 4 days. The anthers (the male reproductive parts) or styles (female reproductive parts) are situated underneath the disk.

Flowers last for only a few days and are unisexual, meaning that they can't self-pollinate. Pollination is done with the help of insects, that have to first visit a male and then a female flower. This means that successful pollination requires opposite sex flowers to be in close proximity. However, even single R.arnoldii flowers are a rare sight. This, in combination with their short life, results in very low rates of successful pollination.

Photo showing R. arnoldii flowers and buds
Rafflesia arnoldii flower and buds

The fruits produced by the plant are round and filled with smooth flesh that contains thousands of hard coated seeds, which are eaten and spread by treeshrews (small rodent-like mammals).

Image of a treeshrew (Anathana ellioti)
A treeshrew
(Anathana ellioti)


Currently, there are two known varieties of R.arnoldii:
  • The most common variety is the R. arnoldii var. arnoldii, found in Sumatra and Borneo
  • The second is the R. arnoldii var. atjehensis, occurring exlusively in north Sumatra.
The main difference between the two varieties is that in R. arnoldii var. atjehensis, the central disk (known as ramenta) is partly missing at the base of the central column.

Video showing the flower of R.arnoldii

Conservation Status
Due to their hard to find nature, not much is known about the plant's overall population. Nevertheless, it is speculated that the populations are continuously declining due to ongoing habitat destruction. Some environmentalists are trying to emulate the species' environment in order to stimulate their recovery, with little - if any - success as of today. Additionally, in Malaysia authorities are trying to help the plant's survival by allowing people who have it on their property to charge small fees to anyone wishing to see it, in an effort to discourage locals from destroying or selling the flowers before they manage to reproduce.

Medicinal Uses
Locals use the flower buds in a variety of ways, including:
  • During childbirth for an easier delivery and a faster recovery
  • As an aphrodisiac
These uses have no medical proof to support them.

Image showing a R.arnoldii specimen from the Kyoto Botanical Garden
Specimen of R.arnoldii at the Kyoto Botanical Garden

Interesting facts about Rafflesia arnoldii
- R.arnoldii is one of the three national flowers of Indonesia. It was officially recognized as a national "rare flower" (Indonesian: puspa langka) in Presidential Decree No. 4 in 1993. The other two are the white jasmine (Jasminum sambac) and the moon orchid (Phalaenopsis amabilis).
-  Rafflesia arnoldii was officially described in 1821 by Robert Brown, (1773 - 1858), a Scottish botanist and palaeobotanist who made important contributions to botany, largely through his pioneering use of the microscope.

Image showing a white jasmine and a moon orchid
White jasmine (left) and moon orchid (right)
the other two national flowers of Indonesia

References & Further Reading
- Olah, L. (1960). Cytological and Morphological Investigations in Rafflesia arnoldi R. Br. Bulletin of the Torrey Botanical Club, 87 (6) DOI: 10.2307/2482906
- Nikolov LA, Endress PK, Sugumaran M, Sasirat S, Vessabutr S, Kramer EM, & Davis CC (2013). Developmental origins of the world's largest flowers, Rafflesiaceae. Proceedings of the National Academy of Sciences of the United States of America, 110 (46), 18578-83 PMID: 24167265
- Mabberley, D.J. (1999). Robert Brown on Rafflesia. Blumea 44: 343-350.
- Schmid, R., & Nais, J. (2003). Rafflesia of the World Taxon, 52 (4) DOI: 10.2307/3647375

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