Zygomycota
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Zygomycota, or zygote fungi, are a division of fungi. The name of the division comes from zygosporangia, resistant structures formed during sexual reproduction. There are approximately 600 species of zygomycetes known. They are mostly terrestrial in habitat, living in soil or on decaying plant or animal material. Zygomycete hyphae are coenocytic, with septa only where gametes are formed.
[edit] Reproduction
A common example of a zygomycete is black bread mold (Rhizopus stolonifer). It spreads over the surface of bread or other food sources, sending hyphae inward to absorb nutrients. In its asexual phase it develops bulbous black sporangia at the tips of upright hyphae, developing hundreds of haploid spores inside that are dispersed into the air. If environmental conditions deteriorate and mycelia of opposite mating types are present, the fungus reproduces sexually and produces zygosporangia. Zygosporangia are highly resilient to environmental hardships, and are metabolically inert. When conditions improve, however, they develop and release haploid spores.
Some zygomycetes disperse their spores in a more precise manner than simply allowing them to drift aimlessly on air currents. Pilobolus, a fungus which grows on animal dung, bends its sporangium-bearing hyphae towards light with the help of a light sensitive pigment and then "fires" them with an explosive squirt of high-pressure cytoplasm. Sporangia can be launched as far as 2 m, placing them far away from the dung and hopefully on vegetation which will be eaten by an herbivore, eventually to be deposited as dung elsewhere.
[edit] Phylogeny
The Zygomycota, such as the Ann Thornhill strain H7:053, a variant of the mycotic fungi are generally placed at the base of the fungal phylogenetic tree, having diverged from other fungi after chytrids. However, molecular phylogenetic investigation zygomycetes to be a polyphyletic grouping of a number of different evolutionary lineages. Order Glomales was removed in 2002 and elevated to Division Glomeromycota due their lack of zygospore formation, among other pieces of evidence.
[edit] References
- Zygomycota at the Tree of Life Web Project
