Mucorales
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Chaetocladiaceae |
Mucorales are the largest and best studied order of Zygomycete fungi.
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[edit] Systematics
The order contains 12-13 families (see the taxbox->), 56 genera and approximately 300 species. The traditional system has been built on studies of morphology, development and ecology. But now, as molecular data accumulate, the old system has proved to be quite artificial. For example, the Mucoraceae is believed to be polyphyletic, as well as Thamnidiaceae, Chaetocladiaceae and Radiomycetaceae. Even some of the genera, (such as Mucor, Absidia and Backusella) appear to be polyphyletic, with their species distributed among different clades. But as the new classification schemes are not complete yet, the traditional systematics is still largely in use.
[edit] Characteristics
Mucorales have a fast-growing mycelium without septae in hyphae (multiperforate septa are present only where sporangiophores and gametangia grow). The hyphae grow mostly inside the substrate. Outside substrate grow the so called stolon hyphae, that attach to substrate by means of rhizoids in places where sporangiophores grow (Rhizoid hyphae). Sporangiophores are upright (simple or ramified) hyphae that form sporangia at their tips.
[edit] Life-cycle
Asexual mitospores (spores formed by mitosis) form within the sporangia (thousands of spores) or sporangioles (single spore or a few). They are released when mature by the disintegration of sporangium wall. The sporangioles containing one spore can have their wall fused with spore wall. In that case, the whole sporangioles separate from the fungus, and are carried by wind like conidia.
Germination of these spores forms the haploid hyphae of a new mycelium. Asexual reproduction occurs continuously.
Sexual reproduction occurs only when opposite mating types (designated + and -) come in contact. Then special cells become gametes that fuse forming a zygote. The zygote develops a resistant cell wall, forming a zygospore, the characteristic that gives its name to this group of fungi. Subsequently, the zygospore germinates and forms a sporangiophore whose sporangium produces both + and - haploid spores.
[edit] Ecology
Most Mucorales are saprotrophic on organic substrates (such as fruit, soil, and dung), some species are also parasites of animals, plants and fungi.
Mucorales include also a few species causing human disease zygomycosis, as well as allergic reactions.
