xanthocomically: An Introduction to Fungi The first thing to…

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Fungal hyphae, with spores. Hyphae are the long branches of growth.


Example of a macroscopic fruiting body–a mushroom!


Yeast form of a fungal species



Development of conidia (a type of spore) from a hyphal tip


Aseptate and septate hyphae


Eukaryotic tree of life, with a fungal emphasis. True fungi include many phylla, but NOT slime molds and oomycetes.

xanthocomically:

An Introduction to Fungi

The first thing to know about fungi is that their taxonomy is kind of a nightmare. Previously, fungi had been categorized by form and habit, which DNA analysis is now suggesting does not accurately represent the relationships between species. So any taxonomy discussed here may be inaccurate, or may change as genetic data becomes available. Please feel let me know if you find a updated classification. 

Anyway, let’s get on to some fungal basics. This will just be a summary of some important characteristics of fungi.

Nutrition: Fungi are heterotropic, meaning that they consume other organisms or compounds for energy and nutrients. The excrete exoenzymes to digest their substrate and absorb the useful molecules and components.

Vegetative State: Generally, fungi are found as a thallus growing on a substrate. The thallus (Greek: shoot, twig) is the body of the fungi, made up of hyphal strands, which are non-differentiated, vegetative branches of growth. The thallus is also  known as the mycelium. Fungi are filamentous because this increases their surface area for the absorption of nutrients. The hyphae can have crosswalls (ie, be spetate) or have no crosswalls (ie, be aseptate or coenocytic). Most septate hyphae have pores in the septa to allow for the cytoplasm and other molecules to flow between cells.

Some fungi are found in non-filamentous forms. These single-celled organisms are called yeasts, and reproduce through budding or fission. Some species have a yeast and a hyphal form, and can switch between the two depending on their environment.

Cell Wall: The cell wall of the true fungi ALWAYS contains chitin. Glucans and other molecules may also be found. (Chitin is also found in the exoskeleton of arthropods.) The membranes also contain ergosterol, which serves the same function as cholesterol in animal cells by making membranes more fluid and easily permeable.

Domain of Life: Fungi are members of the domain Eucara, like animals and plants. They are actually more closely related to animals than they are to plants. 

Life Cycle: Although all are eukaryotic, fungi nuclei vary greatly from one another. Species may be uninucleate or multinucleate, may have haploiddiploid, or dikaryotic (possessing two unfused nuclei from different parents in the same hyphal compartment). The reproduction may be simple or complex, and require one, several, or no hosts. Reproduction may be sexual, asexual, parasexual, or a combination of different strategies in the same species or individual.

Propagules: Fungi are propagated by microscopic spores. Some species produce millions of spores, and fungal spores can be found in the air, the fossil record, water, and food. Spores are generally nonmotile, with the Chitryidomycota being an exception to this rule. Possessing filamentous hyphae allows for the easy production, fragmentation, and dissipation of both sexual and asexual spores.

Sporocarps: Sporocarps are the reproductive structures of fungi. They can be macroscopic (like mushrooms) or microscopic (like conidiophores). Often, especially in the Ascomycetes and Basidiomycetes (the “higher fungi”), the sporocarps may be useful for species identification. 

Habitat: Fungi are found pretty much everywhere. If it is an environment on land or in fresh or salt water, fungi can be found there.

Ecological Significance: Fungi play important roles as saprotrophs (consumers of dead material), mutualists (such as through the formation of mycorrhizae with plant roots), and parasites. They have great economic significance for culinary reasons, as food spoiling agents, as pests, and as pest control. 

Conclusion: A very limited number of fungal species have been named a described. It is estimated that to date, only 5-10% of all fungi have been discovered. This means that it is very common for even the casual mycologist to find a new species! Fungi are a very diverse and important group of organisms, although not very well understood or appreciated by the general public. I hope this series will be informative.

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