Rhizanthella
Encyclopedia
Rhizanthella, commonly known as underground orchids, is a small epiparasitic, achlorophyllous, subterranean genus
of orchid endemic native to Australia
. It is abbreviated in trade journals as Rhi.
These orchids are rare and their status is considered vulnerable to critical, mostly due to loss of habitat
. They live underground in symbiosis
with mycorrhiza
l fungi. These subterranean rhizome
s or tuber
s are short and thickened, without roots, serving as storage for the orchid. The leaves are absent.
When the orchid prepares to flower, the solitary inflorescence
s break through the surface, beneath the leaf litter. The terminal inflorescence is racemose. It gives rise to a cluster of small, tubular, hermaphroditic flower
s. The fragrant flowerheads are about 5 cm wide and contain numerous, inward-facing, small flowers.
Pollination is carried out by small flies
or insect
s, even underground by termite
s or gnat
s. The fruit is a fleshy, indehiscent drupe
with about 250 minute seeds.
Their discovery in 1928 caused such an excitement among orchid lovers, that a wax model had to be toured around Britain.
Genus
In biology, a genus is a low-level taxonomic rank used in the biological classification of living and fossil organisms, which is an example of definition by genus and differentia...
of orchid endemic native to Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
. It is abbreviated in trade journals as Rhi.
These orchids are rare and their status is considered vulnerable to critical, mostly due to loss of habitat
Habitat (ecology)
A habitat is an ecological or environmental area that is inhabited by a particular species of animal, plant or other type of organism...
. They live underground in symbiosis
Symbiosis
Symbiosis is close and often long-term interaction between different biological species. In 1877 Bennett used the word symbiosis to describe the mutualistic relationship in lichens...
with mycorrhiza
Mycorrhiza
A mycorrhiza is a symbiotic association between a fungus and the roots of a vascular plant....
l fungi. These subterranean rhizome
Rhizome
In botany and dendrology, a rhizome is a characteristically horizontal stem of a plant that is usually found underground, often sending out roots and shoots from its nodes...
s or tuber
Tuber
Tubers are various types of modified plant structures that are enlarged to store nutrients. They are used by plants to survive the winter or dry months and provide energy and nutrients for regrowth during the next growing season and they are a means of asexual reproduction...
s are short and thickened, without roots, serving as storage for the orchid. The leaves are absent.
When the orchid prepares to flower, the solitary inflorescence
Inflorescence
An inflorescence is a group or cluster of flowers arranged on a stem that is composed of a main branch or a complicated arrangement of branches. Strictly, it is the part of the shoot of seed plants where flowers are formed and which is accordingly modified...
s break through the surface, beneath the leaf litter. The terminal inflorescence is racemose. It gives rise to a cluster of small, tubular, hermaphroditic flower
Flower
A flower, sometimes known as a bloom or blossom, is the reproductive structure found in flowering plants . The biological function of a flower is to effect reproduction, usually by providing a mechanism for the union of sperm with eggs...
s. The fragrant flowerheads are about 5 cm wide and contain numerous, inward-facing, small flowers.
Pollination is carried out by small flies
Fly
True flies are insects of the order Diptera . They possess a pair of wings on the mesothorax and a pair of halteres, derived from the hind wings, on the metathorax...
or insect
Insect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
s, even underground by termite
Termite
Termites are a group of eusocial insects that, until recently, were classified at the taxonomic rank of order Isoptera , but are now accepted as the epifamily Termitoidae, of the cockroach order Blattodea...
s or gnat
Gnat
A gnat is any of many species of tiny flying insects in the Dipterid suborder Nematocera, especially those in the families Mycetophilidae, Anisopodidae and Sciaridae.In British English the term applies particularly to Nematocerans of the family Culicidae...
s. The fruit is a fleshy, indehiscent drupe
Drupe
In botany, a drupe is a fruit in which an outer fleshy part surrounds a shell of hardened endocarp with a seed inside. These fruits develop from a single carpel, and mostly from flowers with superior ovaries...
with about 250 minute seeds.
Their discovery in 1928 caused such an excitement among orchid lovers, that a wax model had to be toured around Britain.
Reference works
- George, A. S. (1981). Rhizanthella-The Underground Orchid of Western Australia. Proceedings of the Orchid Symposium, 13th International Botanical Congress 77-78.
- Dixon, K. W., et al. (1990). The Western Australian fully subterranean orchid Rhizanthella gardneri. Orchid Biology, Reviews and Perspectives. V. J. Arditti. Portland, Oregon, Timber Press. 5: 37-62.
- Dixon, K. (2003) Underground Orchids on the Edge. Plant Talk, 31: 34-35.
- Jones, D.L. & Clements, M.A. (2006). Rhizanthella omissa, a new species of underground orchid from south eastern Australia. The Orchadian, vol. 15, no. 3, pp. 131-133.
Further reading
- Hoffman, N., Brown, A. (1998). Orchids of South-west Australia. University of Western Australia Press, Nedlands.Rev. 2nd ed. with suppl. ISBN 1876268182
- Jones, David L. (2006). A complete guide to native orchids of Australia: including the island territories. Frenchs Forest. ISBN 1-8770-6912-4.
- Underground orchid - Rhizanthella gardneri at ARKive.org (includes photographs)