Rafflesia

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Rafflesia
Rafflesia sp.

Rafflesia sp.

Systematics
Nuclear eudicotyledons
Rosids
Eurosiden I
Order : Malpighiales (Malpighiales)
Family : Rafflesiaceae (Rafflesiaceae)
Genre : Rafflesia
Scientific name
Rafflesia
R.Br.

The Rafflesia ( Rafflesia ) are a genus of plants within the Rafflesia family (Rafflesiaceae). The best-known species , the giant rafflesia ( Rafflesia arnoldii ), has the largest flowers in the plant kingdom.

Description and ecology

Rafflesia spec. on Borneo
Rafflesia just before flowering, Khao Sok (Thailand)
Rafflesia withered, Khao Sok (Thailand)
Detail of the flower
Rafflesia Kelantanesis Gan, Cameron Highlands (cigarette pack for comparison)

The plants are full parasites that, with the exception of the flowers, live completely within their host plant . There they only consist of a mycelium-like network interspersed with haustoria . Roots , shoots and leaves are not developed. The specific host plants are species of the liana- forming genus Tetrastigma from the vine family (Vitaceae). The bloom is short-lived and disintegrates into black, tough mucus after a few days.

Rafflesien are dioeciously separated sexes ( diocesan ). The flowers formed outside the host are usually on the ground, but also appear up to about 1 meter in height. Directly below them are small scales that may represent reduced bracts or sepals . The inflorescence consists of five leathery petals up to 1 centimeter thick . When fully developed, the diameter of the flowers is between 13 centimeters and almost a meter, depending on the species. They imitate carrion in color and smell and thus attract insects , mainly flies , to pollinate . The central column of the male flowers has openings through which pollinators can enter the flower. Passed through translucent windows and hair set up like a trap , the insects get into a position in which the pollen in a viscous liquid is attached to them. To get to the female flowers, the pollinators have to squeeze through a gap into which the pollen at the scars are stripped. So only insects of a certain size are suitable as pollinators. Fruits are seldom formed, take about a year to ripen, and can contain several thousand seeds . They are probably spread by rodents ( squirrels ; zoochory ).

Ecosystem

The highly specialized plants are only rarely found in nature and, as they are dependent on a complex functioning ecosystem , are considered endangered with all species.

  • Depending on the species, they are dependent on very specific host plants. If the hosts are eliminated or damaged by deforestation , by "clearing up" or by overcrowding the forest, the Rafflesia cannot develop.
  • The flowers need an evenly warm and humid climate . Too little moisture allows them to dry out prematurely, too high moisture to rot prematurely.
  • The flowers take several months (up to a year) to develop, but then only last a few (4 to 7) days. This means that the probability that a male flower and a nearby female flower are open at the same time is very low.
  • The flowers can only be pollinated by insects of a certain size. These in turn are dependent on a functioning ecosystem in which carrion ( left behind by predators ) occurs, which they need for their reproduction.
  • The rodents that spread the seeds also need a functioning ecosystem in which they can find, for example, sufficient protection and food.

Since the flowers attract a lot of attention due to their size, a tourism to Rafflesia to well-known locations has emerged. In some cases, this has led to protective measures such as fences and logging bans being taken to preserve the source of income generated by tourism.

Systematics and distribution

The genus Rafflesia was established by Robert Brown . The scientific generic name Rafflesia honors its discoverer, Sir Thomas Stamford Raffles .

The distribution area of ​​Rafflesia extends in Southeast Asia from the Malay Peninsula ( Thailand , Malaysia ) via Sumatra and Java ( Indonesia ) and Borneo (Malaysia, Indonesia, Brunei ) to the Philippines . The plants grow there in tropical rainforests at altitudes of 500 to 700 meters.

Since the plants have no organs apart from the flowers that allow a comparative analysis, the systematic position of the genus Rafflesia was previously unclear. It is traditionally managed in its own plant family Rafflesiaceae . DNA analyzes have shown that Rafflesia and its relatives branch off at the base of the family tree of the milkweed family (Euphorbiaceae). In response to this, the separation of the Peraceae from the Euphorbiaceae was proposed, which would have the consequence that the other milkweed plants would remain monophyletic and at the same time would be more uniform with regard to the anatomy of the fruit and the seed coat . The relationships can be illustrated by the following cladogram :




Euphorbiaceae s. st.


 Rafflesiaceae 


Rafflesia


   

Rhizanthes



   

Sapria




   

Peraceae (suggested)



The research result is so surprising because, in clear contrast to the Rafflesia family, a tendency to shrink the flowers can be observed in the milkweed family, which in the genus Euphorbia reaches an extreme with tiny, individual bare stamens and individual bare ovaries.

species

The 20 species since Meijer 1997 differ in the size, shape, color and texture of their flowers. The other organs, i.e. the network growing in the host plants, have so far hardly been examined comparatively.

Here is a selection of the types:

The following species have been described as new since 2010:

Another species was described after a single bud. It remains to be checked whether there is actually a species of its own:

  • Rafflesia witkampi Coord . : Borneo: Sekerat Mts., Northeast Kalimantan, Indonesia

literature

  • Ladislao V. Olah: Cytological and Morphological Investigations in Rafflesia arnoldi R. Br. In: Bulletin of the Torrey Botanical Club. Volume 87, Issue 6, 1960, pp. 406-416, doi : 10.2307 / 2482906 .
  • Reed S. Beaman, Pamla J. Decker, John H. Beaman: Pollination of Rafflesia (Rafflesiaceae). In: American Journal of Botany. Volume 75, Issue 8, 1988, pp. 1148-1162, doi : 10.2307 / 2444098 .
  • P. Simons: Rafflesia, the world's largest flower. In: Biological Sciences Review. Volume 5, Issue 1, ISSN  0953-5365 , 1992, pp. 7-9
  • Willem Meijer: Rafflesiaceae. In: Cornelis Kalkman et al. (Ed.): Flora Malesiana. Series 1: Spermatophyta. Issue 13: Rafflesiaceae, Boraginaceae, Daphniphyllaceae, Illiciaceae, Schisandraceae, Loranthaceae, Viscaceae. Rijksherbarium - Hortus Botanicus, Leiden 1997, ISBN 90-71236-33-1 , pp. 1-42, ( digitized version ).
  • Jamili Nais: Rafflesia of the World. Sabah Parks, Kota Kinabalu 2001, ISBN 983-812-042-1 .

Individual evidence

  1. ↑ CC Davis, M. Latvis, DL Nickrent, KJ Wurdack, DA Baum: Floral gigantism in Rafflesiaceae. In: Science , published online January 11, 2007.
  2. ↑ The Peraceae Family at the Angiosperm Phylogeny website .
  3. ^ The International Plant Names Index. [1]

Web links

Commons : Rafflesia ( Rafflesia )  - collection of images, videos and audio files