Geosiphon pyriformis
| Geosiphon | |
|---|---|
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| Scientific classification | |
| Kingdom: | Fungi |
| Division: | Glomeromycota |
| Class: | Glomeromycetes |
| Order: | Archaeosporales |
| Family: | Geosiphonaceae |
| Genus: |
Geosiphon F.Wettst. (1915) |
| Type species | |
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Geosiphon pyriformis (Kütz.) F.Wettst. (1915) |
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Geosiphon is a genus of fungi in the family Geosiphonaceae. The genus is monotypic, containing the single species Geosiphon pyriformis, first described by Kützing in 1849 as Botrydium pyriforme. In 1915, Von Wettstein characterized Geosiphon pyriforme as a multinucleate alga containing endosymbiotic cyanobacteria, although he also noted the presence of chitin, a component of fungal cell walls. In 1933, Knapp was the first to suggest the fungal origin of the species and described it as a lichen with endosymbiotic cyanobacteria. It is the only member of the Glomeromycota to not form a symbiosis with terrestrial plants in the form of arbuscular mycorrhiza.
Geosiphon pyriformis is known for being the symbiont of . The Geosiphon- symbiosis, as by modern definitions, is not a lichen, since it is an intracellular association. Also, by functional and evolutionary implications it is more comparable to the arbuscular mycorrhiza symbioses than to lichens.
The Geosiphon- symbiosis is the only known fungal endosymbiosis with cyanobacteria and is characterised by a "siphonal bladder" that is made of a swollen fungal hypha, 0.5–2 mm in size and growing on the soil surface. The upper 2/3 of the "bladder" contains the Nostoc filaments and Nostoc heterocysts, the lower 1/3 is filled with lipid droplets.
The fungal spores are 250 micrometres in diameter, formed at the end of one hypha, or intercalarly (within a hyphae) and resemble those of members of the Glomeromycota.
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