Rhizanthella gardneri
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Rhizanthella gardneri , illustration |
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Rhizanthella gardneri is a plant type from the family of orchids (Orchidaceae). It was first described in 1928. The little-explored species is native to Australia, lives completely underground and is extremely rare.
features
Vegetative habit
Rhizanthella gardneri is a root and (deciduous) leafless plant that grows underground. It has completely given up photosynthesis and accordingly no longer forms chlorophyll , instead it lives myco-heterotrophic .
The 10 to 20 millimeter thick and 30 to 50 millimeter long, branched and brittle rhizome of the plants lies 6 to 12 centimeters below the surface of the earth, is slightly hairy, white and fleshy and covered with isolated triangular lower leaves that are between 1 and 3 centimeters long and 5 to 10 millimeters wide. If injured, it gives off a distinctly noticeable formalin odor .
In addition to sexual reproduction via seeds, Rhizanthella gardneri also reproduces vegetatively, it forms up to three offshoots from the rhizome .
blossom
From April, after heavy rainfall in the Australian summer, a 40 to 60 millimeter long flower stalk grows from the rhizome to just below the surface of the earth , with a single so-called capitulum at the end , which blooms between May and July. It is an upright, concave flower head with a diameter of 20 to 50 millimeters, that of six to twelve, standing in two circles, white, fleshy, 10 to 35 millimeters long and 5 to 10 millimeters wide, egg-shaped to oblong egg-shaped overlapping each other bracts is enclosed. Its tips occasionally break through the surface of the earth, then darken reddish and bend back. The bracts are three- to seven-veined.
The 8 to 150 short, tubular and fragrant single flowers are 5 to 6 millimeters long and 5 millimeters wide, whitish to dark red-brown and arranged in a solid spiral of 4 to 5 rings pointing towards the center in the flattened and slightly widened capitulum.
The outer and inner bracts are fused in the lower half, free above, but overlapping each other. The labellum is narrow, heart-shaped, 1.5 to 2 millimeters long and 1.5 millimeters wide, strongly curved, smooth and firm, deep red at the edges like the tip. The upright, cylindrical column is almost as long as the outer bracts. The anthers are upright, blunt and flattened at the tip, the egg-shaped stigma protrudes horizontally and is comparatively large.
The exact process of pollination is still largely unknown; sciarid gnats , gall gnats , braconidae , humpback flies of the genus Megaselia and termites of the genus Drepanotermes are possible pollinators . These dig through the thin, loose layer of soil above the flower head and thus reach the flowers.
Fruit and seeds
Even after flowering, the stem does not lengthen and the fruits ripen underground. Each of the pollinated flowers forms a brown, berry-like , fleshy fruit, which can take up to seven months to ripen and which contains between 20 and 150 relatively large seeds , which is unusual for an orchid . The seeds may be spread by bag mammals , which eat the fruit and excrete the seeds with the droppings elsewhere.
Way of life
Like most orchids, Rhizanthella gardneri also uses the connection to a mycorrhizal fungus to feed itself. In this case, however, it is not a symbiosis , but a special form of parasitism , as the fungus does not benefit from the connection: As a so-called mykoheterotrophic plant, Rhizanthella gardneri feeds on the fungus, which in turn has a symbiotic relationship with the surrounding area Myrtle heather of the species Melaleuca uncinata .
Unusually for an orchid, Rhizanthella gardneri does not need mycorrhiza for embryonic development from a seed; the seeds germinate without being attacked by a mycorrhizal fungus. Only the protocorm (the germinal nodule) is then infected on its hairs by the mycorrhizal fungus Thanatephorus gardneri , the hyphae of the fungi penetrate the cortical cells of the rhizome ( endomycorrhiza ). If the infection does not occur, the seedlings will no longer thrive. When the egg-shaped protocorm has reached a diameter of 1.0 to 1.5 centimeters, the rhizome begins to form, which grows 1.4 to 2.2 millimeters per week. The plant can reach flowering maturity within 15 months of germination.
Distribution and habitat
The species is known from only six locations in two isolated areas of Western Australia , on the one hand in the Wheatbelt region around Corrigin and on the other 260 km away from it at Munglinup near the south coast. It grows at altitudes of 300 to 400 meters in nutrient-poor, well-drained, sandy loam soils, each at a distance of 20 to 30 centimeters from fully grown Melaleuca uncinata , in the habitats there are also isolated acacias and eucalyptus . The average annual precipitation values are 500 to 600 millimeters, in the drought years around the turn of the millennium this value sank to 200 millimeters. The temperatures fluctuate between 0 and 30 ° C.
Botanical history
On May 23, 1928, a farmer named John Trott discovered 36 specimens of this orchid while plowing an area designated for agricultural use. Dr. Richard Sanders Rogers, known as an expert on Australian orchids, named the orchid after the then President of Western Australia, Charles Austin Gardner , Rhizanthella gardneri . The discovery caused such a stir that a specially made wax model of the plant was presented in a traveling exhibition in England.
By 1959 there were six more accidental finds during plowing work, after a long break the plant could then be observed undisturbed in its natural location for the first time in 1979. By means of targeted searches, five more populations were found up to 1985; no further locations have been known since then. Until 1984 the species was the only known of its genus, Rhizanthella slateri only followed in 1984 ( described as Crypthanthemis slateri in 1932 ) and Rhizanthella omissa in 2006 .
Status and exposure
At all locations, Rhizanthella gardneri is only represented in a very small number of individuals. Whereas in the 1980s a total of 150 blooming individuals were found at the six locations, including an occurrence with over 100 plants, in 2002 censuses only 19 blooming plants were found, with the largest occurrence comprising 10 individuals and three of the occurrences are considered to be in bad shape.
The main risk factors are the few available habitats, the extremely fragmented locations and - triggered by the droughts in the region - the decline in the host species Melaleuca uncinata and the salinisation of the groundwater in the Wheatbelt region . Due to the extremely small populations, human curiosity also has a harmful influence, as the few plants are permanently disturbed by repeated searches (soil compaction, drying out of exposed flowers).
Three of the six known locations have already been placed under protection and a special program, which was set up from 2003 to 2008, was initiated to ensure the survival of the species (among other things by setting up a sperm bank and taking DNA samples). However, the first targeted application of some previously removed seeds to suitable locations failed.
Rhizanthella gardneri is not explicitly mentioned in the Washington Convention on the Protection of Species (CITES), but is listed as a wild orchid in Appendix 2 . In Germany, all Rhizanthella species are strictly or particularly protected under the Federal Nature Conservation Act with protection status B. On the red list of the IUCN , the species is since 1997 'at risk' ( vulnerable ) out.
swell
- Sofi Mursidawati: Mycorrhizal association, propagation and conservation of the myco-heterotrophic orchid Rhizanthella gardneri. Master's thesis , University of Western Australia, 2004.
- Andrew Brown, Andrew Batty, Mark Brundrett, Kingsley Dixon: Underground Orchid (Rhizanthella gardneri) Interim Recovery Plan 2003–2008. (PDF; 354 kB) Interim Recovery Plan No. 127, February 2003, Department of Conservation and Land Management, Western Australian Threatened Species and Communities Unit (WATSCU).
- David L. Jones: A Complete Guide to Native Orchids of Australia. New Holland, Frenchs Forest 2006, ISBN 1-877069-12-4 .
- Noel Hoffman, Andrew Brown: Orchids of South-west Australia. University of Western Australia Press, Nedlands 1998, ISBN 1-876268-18-2 .
- JH Warcup: Rhizanthella gardneri (Orchidaceae), its Rhizoctonia Endophyte and Close Association with Melaleuca uncinata (Myrtaceae) in Western Australia. In: New Phytologist. 99, No. 2, February 1985, pp. 273-280.
- Jonathan R. Leake: The Biology of Myco-Heterotrophic ('Saprophytic') Plants. In: New Phytologist. 127, No. 2, 1994 ( doi : 10.1111 / j.1469-8137.1985.tb03656.x ), pp. 171-216.
- Underground orchid (Rhizanthella gardneri) at Wildscreen Arkive (English).
- Thanatephorus gardneri Warcup. Entry on mycorrhizal fungus in the Fungorum Index.
- Thanatephorus gardneri Warcup. Entry on the synonymy of the mycorrhizal fungus in the Interactive Catalog of Australian Fungi.
Individual evidence
- ^ David L. Jones: Native Orchids of Australia. Reed, Frenchs Forest 1988, ISBN 0-7301-0189-4 .
- ^ Underground orchid (Rhizanthella gardneri) - Description at arkive.org (English) ( Memento from January 11, 2008 in the Internet Archive ).
- ↑ Rhizanthella gardneri. Entry at Species + / CITES, last accessed on November 2, 2017.
- ↑ Rhizanthella spp. in the Scientific Information System for International Species Conservation (WISIA) of the Federal Agency for Nature Conservation, accessed on November 2, 2017.
- ↑ KS Walter, HJ Gillett: 1997 IUCN Red List of Threatened Plants. IUCN, World Conservation Union, Cambridge 1998, p. 721.
Web links
- Underground orchid (Rhizanthella gardneri). Location photos at Wildscreen Arkive (English)
- Rhizanthella gardneri - Underground Orchids. Numerous detailed photos at The Species Orchid Society of Western Australia (Inc) (private homepage, English)
- Parasites from the underworld. Scientists have examined the chloroplast genome of a species of orchid. Pflanzenforschung.de, March 3, 2011
