Zygomycota

Zygomycota, or zygote fungi, are a phylum of fungi. The name of the phylum comes from zygosporangia, where resistant spherical spores are formed during sexual reproduction. Approximately 600 species of zygomycetes are known. They are mostly terrestrial in habitat, living in soil or on decaying plant or animal material. Zygomycete hyphae may be coenocytic, forming septa only where gametes are formed or to wall off dead hyphae.

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Reproduction

A common example of a zygomycete is black bread mold (Rhizopus stolonifera), a member of the Mucorales. It spreads over the surface of bread and other food sources, sending hyphae inward to absorb nutrients. In its asexual phase it develops bulbous black sporangia at the tips of upright hyphae, each containing hundreds of haploid spores. If the mycelia of complementary mating types are present, the fungus reproduces sexually and produces zygosporangia. Zygosporangia are typically thick-walled, highly resilient to environmental hardships, and are metabolically inert. When conditions improve, however, they germinate to produce a sporangium or vegetative hyphae.

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 sporangiophores 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 2m, placing them far away from the dung and hopefully on vegetation which will be eaten by an herbivore, eventually to be deposited with dung elsewhere. Different mechanisms for forcible spore discharge have evolved among members of the zygomycete order Entomophthorales.

Phylogeny

The Zygomycota are generally placed near the base of the fungal phylogenetic tree, having diverged from other fungi after chytrids. Molecular phylogenetics reveal that they form a polyphyletic group and could see a split into several new phyla.^[1] The order Glomales was removed in 2001 and elevated to Division Glomeromycota due their lack of zygospore formation, their mycorrhizal habit, and lack of DNA sequence homology.

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