Zygomycota
| Zygomycota | |
|---|---|
 |
|
| Sporangium of a Phycomyces sp. | |
| Scientific classification | |
| Kingdom: | Fungi |
| Division: |
Zygomycota C. Moreau 1954 (informal) |
| Class: |
Zygomycetes Winter 1881 |
| Orders | |
Zygomycota, or zygote fungi, is a division of fungi. Approximately 1050 species are known. They are mostly terrestrial in habitat, living in soil or on decaying plant or animal material. Some are parasites of plants, insects, and small animals, while others form symbiotic relationships with plants. Zygomycete hyphae may be coenocytic, forming septa only where gametes are formed or to wall off dead hyphae.
The name Zygomycota refers to the zygosporangia characteristically formed by the members of this clade, in which resistant spherical spores are formed during sexual reproduction. Zygos is Greek for "joining" or "a yoke", referring to the fusion of two hyphal strands which produces these spores, and -mycota is a suffix referring to a division of fungi.
The term "spore" is used to describe a structure related to propagation and dispersal. Zygomycete spores can be formed sexually and asexually. Before germination the spore is in a dormant state. During this period the metabolic rate is very low and it may last from a few hours to many years. There are two types of dormancy. The exogenous dormancy is controlled by environmental factors such as temperature or nutrient availability. The endogenous or constitutive dormancy depends on characteristics of the spore itself; for example, metabolic features. In this type of dormancy, germination may be prevented even if the environmental conditions favor growth.
In zygomycetes, mitospores (sporangiospores) are formed asexually. They are formed in specialized structures, the mitosporangia (sporangia) that contain few to several thousand of spores, depending on the species. Mitosporangia are carried by specialized hyphae, the mitosporangiophores (sporangiophores). These specialized hyphae usually show negative gravitropism and positive phototropism allowing good spore dispersal. The sporangia wall is thin and is easily destroyed by mechanical stimuli (e.g. falling raindrops, passing animals), leading to the dispersal of the ripe mitospores. The walls of these spores contain sporopollenin in some species. Sporopollenin is formed out of β-carotene and is very resistant to biological and chemical degradation. Zygomycete spores may also be classified in respect to their persistence:
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