Monotropastrum humile, an obligate myco-heterotroph.

Myco-heterotrophy is a symbiotic relationship between certain kinds of plants and fungi, in which the plant gets all or part of its food from parasitism upon fungi rather than from photosynthesis. A myco-heterotroph is the parasitic plant partner in this relationship. Myco-heterotrophy is considered a kind of cheating relationship and myco-heterotrophs are sometimes informally referred to as "mycorrhizal cheaters". This relationship is sometimes referred to as mycotrophy, though this term is also used for plants that engage in mutualistic mycorrhizal relationships.

[edit] Relationship between myco-heterotrophs and host fungi

Myco-heterotrophic roots of Monotropa uniflora with Russula brevipes mycelium.

Full (or obligate) myco-heterotrophy exists when a non-photosynthetic plant (a plant largely lacking in chlorophyll or otherwise lacking a functional photosystem) gets all of its food from the fungi that it parasitizes. Partial (or facultative) myco-heterotrophy exists when a plant is capable of photosynthesis, but parasitizes fungi as a supplementary food supply. There are also plants, such as some orchid species, that are non-photosynthetic and obligately myco-heterotrophic for part of their life cycle, and photosynthetic and facultatively myco-heterotrophic or non-myco-heterotrophic for the rest of their life cycle.^[1] Not all non-photosynthetic or "achlorophyllous" plants are myco-heterotrophic ' some non-photosynthetic plants like dodder directly parasitize the vascular tissue of other plants.^[2]

In the past, non-photosynthetic plants were mistakenly thought to get food by breaking down organic matter in a manner similar to saprotrophic fungi. Such plants were therefore called "saprophytes". It is now known that no plant is physiologically capable of direct breakdown of organic matter and that in order to get food, non-photosynthetic plants must engage in parasitism, either through myco-heterotrophy or direct parasitism of other plants.^[3][4]

The interface between the plant and fungal partners in this association is between the roots of the plant and the mycelium of the fungus. Myco-heterotrophy therefore closely resembles mycorrhiza (and indeed is thought to have evolved from mycorrhiza),^[3] except that in myco-heterotrophy, the flow of carbon is from the fungus to the plant, rather than vice versa.^[5][6]

Most myco-heterotrophs can therefore be seen as ultimately being epiparasites, since they take energy from fungi that in turn get their energy from vascular plants.^[3][4][7] Indeed, much myco-heterotrophy takes place in the context of a common mycorrhizal network, in which plants use mycorrhizal fungi to exchange carbon and nutrients with other plants.^[4] In these systems, myco-heterotrophs play the role of "mycorrhizal cheaters", taking carbon from the common network, with no known reward.^[3]

In congruence with ancient reports, it has been recently shown that some myco-heterotrophic orchids can be supported by saprotrophic fungi, exploiting litter- or wood-decaying fungi.^[8] In addition, several green plants (evolutionarily close to myco-heterotrophic ones) have been shown to be able to take carbon from their mycorrhizal fungi, that adds up to their photosynthesis (partial myco-heterotrophy).^[9][10]

[edit] Species diversity of myco-heterotrophs and host fungi

Myco-heterotrophs are found among a number of plant groups. All monotropes and non-photosynthetic orchids are full myco-heterotrophs, as is the non-photosynthetic liverwort Cryptothallus. Partial myco-heterotrophy is common in the Gentian family with a few genera such as Voyria being fully myco-heterotrophic, in photosynthetic orchids, and a number of other plant groups. Some ferns and clubmosses have myco-heterotrophic gametophyte stages.^[1][4][11] The fungi that are parasitized by myco-heterotrophs are typically fungi with large energy reserves to draw on, usually mycorrhizal fungi, though there is some evidence that they may also parasitize parasitic fungi that form extensive mycelial networks, such as Armillaria.^[4]

[edit] Plant Families (with relevant myco-heterotrophic genera)

Monocotyledons

Burmanniaceae (Dioscoreales)

  * Afrothismia - 3 species
  * Apteria - 1 species
  * Burmannia - 60 species
  * Campylosiphon - 1 species
  * Dictyostega - 1 species
  * Gymnosiphon - 50 species
  * Hexapterella - 2 species
  * Thismia - 28 species

Corsiaceae (Liliales)

  * Arachnitis - 1 species
  * Corsia - 20 species
  * Corsiopsis - 1 species

Iridaceae, formerly Geosiridaceae (Asparagales)

  * Geosiris - 1 species

Orchidaceae (Asparagales)

This list only concerns species that are leafless, i.e. or are

losing photosynthetic function.

  * Aphyllorchis - 15 species
  * Corallorhiza - 15 species
  * Cymbidium - 1 species
  * Cyrtosia - 5 species
  * Cystorchis - 8 species
  * Cephalanthera - 1 species
  * Didymoplexis - 10 species
  * Epipogium - 3 species
  * Eulophia - 1 species
  * Galeola - 10 species
  * Gastrodia - 35 species
  * Hexalectris - 7 species
  * Lecanorchis - 20 species
  * Limodorum - 1 species
  * Neottia - 9 species
  * Pterostylis - (as yet, unresolved number)
  * Rhizanthella -  2 species
  * Stereosandra - 1 species
  * Stigmatodactylus - 4 species
  * Wullschlaegelia - 2 species
  * Yoania -  2 species

Peterosaviaceae, also called Melanthiaceae

(Petrosaviales)

  * Petrosavia - 2-4 species
  * Protolirion -  2 species

Triuridaceae (Pandanales), Including

Lacandoniaceae.

  * Lacandonia -  1 species
  * Sciaphila - 31 species
  * Triuris - 3 species

Dicotyledons

Ericaceae (Ericales)

Pyroleae (partially myco-heterotrophic apart from Pyrola

picta ssp. aphylla)

  * Chimaphila - 4-5 species
  * Monoses - 1 species
  * Orthilia - 1 species
  * Pyrola - 35 species

Monotropeae

  * Allotropa - 1 species
  * Hemitomes - 1 species
  * Monotropa - 1 (very variable) species
  * Monotropastrum - 4 species
  * Monotropsis -  1 species
  * Pityopus - 1 species
  * Pleuricospora - 2 species

Pterosporeae

  * Pterospora - 1 species
  * Sarcodes -  1 species

Gentianaceae (Gentianales)

  * Bartonia -  3-4 species
  * Cotylanthera - 4 species
  * Obolaria -  1 species
  * Voyria (including Leiphaimos). 20 species
  * Voyriella - 2 species

Polygalaceae (Fabales)

  * Salomonia (= Epirhixanthes) - 8 species

[edit] References

[edit] Further reading

[edit] External links

• The Strange and Wonderful Myco-heterotrophs The Parasitic Plant Connection, SIU Carbondale, College of Science.
• Wayne's Word Noteworthy Plant For June 1997: Fungus Flowers ' Flowering Plants that Resemble Fungi by WP Armstrong.
• Fungus of the Month for October 2002: Monotropa uniflora by Tom Volk, TomVolkFungi.net
• Martín's Treasure Chest ' images of myco-heterotrophs by mycologist Martín Bidartondo.

Modelling ecosystems - trophic components General Abiotic component – Abiotic stress – Behaviour – Biogeochemical cycle – Biomass – Biotic component – Biotic stress – Carrying capacity – Competition – Ecosystem – Ecosystem ecology – Ecosystem model – Keystone species – List of feeding behaviours – Metabolic theory of ecology – Productivity Producers Autotrophs – Chemosynthesis – Chemotrophs – Foundation species – Mixotrophs – Myco-heterotrophy – Mycotroph – Organotrophs – Photoheterotrophs – Photosynthesis – Photosynthetic efficiency – Phototrophs – Primary nutritional groups – Primary production Consumers Apex predator – Bacterivore – Carnivores – Chemoorganotroph – Foraging – Generalist and specialist species – Herbivores – Heterotroph – Heterotrophic nutrition – Mesopredator release hypothesis – Omnivores – Optimal foraging theory – Predation Decomposers Chemoorganoheterotrophy – Decomposition – Detritivores – Detritus Microorganisms Bacteriophage – Lithoautotroph – Lithotrophy – Microbial food web – Microbial loop – Microbial metabolism – Phage ecology Food webs Cold seeps – Hydrothermal vents – Intertidal – Kelp forests – Lakes – North Pacific Subtropical Gyre – Rivers – San Francisco Estuary – Soil – Tidal pool Trophic effects Ascendency – Bioaccumulation – Biomagnification – Cascade effect – Competitive exclusion principle – Copiotrophs – Dominance – Ecological efficiency – Ecological network – Ecological pyramid – Ecological succession – Energy quality – Energy Systems Language – f-ratio – Feed conversion ratio – Feeding frenzy – Mesotrophic soil – Oligotroph – Paradox of the plankton – Trophic cascade – Trophic level – Trophic mutualism – Trophic state index Defense/counter Antipredator adaptations – Herbivore adaptations to plant defense – Plant defense against herbivores – Predator avoidance in schooling fish   Modelling ecosystems - other components Population ecology Abundance – Allee effect – Depensation – Ecological yield – Effective population size – Intraspecific competition – Logistic function – Malthusian growth model – Maximum sustainable yield – Overpopulation in wild animals – Overexploitation – Population cycle – Population dynamics – Population modeling – Population size – Predator'prey equations – Resilience – Small population size – Stability Species Biodiversity – Density-dependent inhibition – Ecological effects of biodiversity – Ecological extinction – Endemic species – Flagship species – Gradient analysis – Indicator species – Introduced species – Invasive species – Latitudinal gradients in species diversity – Minimum viable population – Occupancy-abundance relationship – Population viability analysis – Rapoport's rule – Relative abundance distribution – Relative species abundance – Species diversity – Species homogeneity – Species richness – Species distribution – Species-area curve – Umbrella species Species interaction Antibiosis – Biological interaction – Commensalism – Community ecology – Ecological facilitation – Interspecific competition – Mutualism Landscape ecology Cross-boundary subsidy – Ecocline – Ecotone – Ecotype – Disturbance – Edge effect – Foster's rule – Habitat fragmentation – Intermediate Disturbance Hypothesis – Island biogeography – Landscape epidemiology – Landscape limnology – Metapopulation – Patch dynamics – Source'sink dynamics Niche Ecological niche – Ecological trap – Ecosystem engineer – Environmental niche modelling – Guild – Habitat – Limiting similarity – Niche apportionment models – Niche differentiation Other components Assembly rules – Bateman's principle – Bioluminescence – Ecological collapse – Ecological debt – Ecological deficit – Ecological energetics – Ecological indicator – Ecological threshold – Ecosystem diversity – Emergence – Kleiber's law – Liebig's law of the minimum – Marginal value theorem – Thorson's rule – Xerosere Other Allometry – Balance of Nature – Biological data visualization – Biogeography – Constructal theory – Ecocline – Ecological economics – Ecological footprint – Ecological forecasting – Ecological humanities – Ecological stoichiometry – Ecopath – Ecosystem based fisheries – Endolith – Evolutionary ecology – Functional ecology – Industrial ecology – Macroecology – Microecosystem – Natural environment – Systems ecology – Theoretical ecology List of ecology topics