THE BASICS
Fungi make up the third-largest kingdom of organisms, Kingdom Fungi.
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Just like plants and animals, fungi are eukaryotic.
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Although most of us have seen fungi before, most fungi are microbes. What we usually think of as fungi (like mushrooms) are actually their fruiting bodies.
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Fungi are monophyletic but other organisms are sometimes grouped with them. Oomycetes (water molds) are an example of this. Just like fungi, these organisms have hyphae but are more closely related to brown algae (kelp).
So what exactly are fungi made of?
Fungi are made of hyphae. These long, threadlike filaments are the main mode of growth for fungi. They grow from a structure called the spitzenkorper found at their tips. In most fungi, hyphae are separated by septa. Septa are spaced in the middle, allowing for some movement between hyphae. Although fragile, hyphae are able to break through asphalt, plant tissue, animal tissue, and many other seemingly impenetrable materials.
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Hyphae organized together are collectively known as mycelium. There are three kinds of mycelium - primary, secondary, and tertiary. Tertiary mycelium is an organized, specialized tissue that we know as the fruiting body of basidiocarps.
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The cell walls of fungi are made of chitin, a substance also found in kingdom Animalia in the exoskeletons of arthropods, beaks of cephalopods, skin of amphibians, and scales of fish.
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How do fungi obtain nutrients?
Fungi are heterotrophs. This means that they require other organisms for energy and proteins. They can’t make their own food from sunlight like plants and algae can, but must digest other organic material for nutrients.
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Fungi digest externally through absorption. They do this by secreting digestive enzymes into the environment to break down complex organic molecules.
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Some fungi are parasitic, this means that they feed on the living tissue of a host. Some examples of parasitic fungi are ergot, Dutch elm disease, and ringworm. Most fungi are saprobic, meaning that they feed on dead tissues or organic wastes. These fungi are known as decomposers - helping to remove leaf litter and other debris that would otherwise build up on forest floors.
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Some fungi are symbiotic. This means they have a mutually beneficial relationship with another organism. Most plants rely on these fungi to obtain nutrients and water from the soil.
Mycorrhizal fungi connect plants (even plants of different species) through their roots. This association is called a mycorrhizal network. A mycorrhizal relationship is usually mutualistic, but can sometimes be parasitic.
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How do fungi reproduce?
There are 3 different strategies fungi can use to reproduce. Some fungi reproduce through sexual reproduction. This introduces genetic variation to the population. Other fungi reproduce through asexual reproduction. This can happen through fragmentation, splitting, or budding. Fungi can also reproduce through parasexual reproduction. This type of reproduction is a strategy unique to fungi and single-celled organisms and allows the organism to transfer genetic material without meiosis or the development of sexual structures.
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Most species of fungi reproduce through a combination of both sexual and asexual reproduction.
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Ascomycota
Ascomycota, or sac fungi, make up the largest phylum of fungi.
Ascomycetes are diverse and include yeasts, truffles, lichen-forming taxa, powdery mildew, and many microscopic species.
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Basidiomycota
Basidiomycota, or club fungi, are what most people think of when asked to describe fungi. It includes three subphyla including Agaricomycotina (mushrooms, puffballs, shelf fungi, and jelly fungi), Ustilaginomycotina (smut fungi), and Pucciniomycotina (rust fungi).
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Chytridiomycota
Chytridiomycota, or chytrids, are a group of saprobic fungi that are sometimes parasitic. Their name is derived from the Greek word for "little pot", a description of the structure that contains unrelased zoospores. Batrachochytrium dendrobatidis and B. salamandrivorans are two chytrid species that cause chytridiomycosis in amphibians.
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Deuteromycota
Deuteromycota, or imperfect fungi, don't quite fit into the traditional taxonomic classification system. This is because the sexual reproductive cycle of these evasive fungi have never been observed. Many of these species are anamorphs of basidiomycetes and ascomycetes.
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Glomeromycota
Glomeromycota, or mycorrhizal fungi, from arbuscular mycorrhizas with the thalli of bryophytes and the roots of vascular plants.
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Zygomycota
Zygomycota, or zygote fungi, make up 1% of all described species of fungi. Their sexual reproduction consists of zygospores produced by zygosporangium, not seen very often in nature.
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Pseudofungi
these fakers are cute, but they aren't fungi
Pseudofungi, or oomycetes and slime molds, coming soon.
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