What are Mushrooms?

In essence, all mushrooms are fungi, but not all fungi are mushrooms!

CLASSIFICATION

To understand what mushrooms are, we first have to know how everything within the living world is classified (figure 1). Within the group Life, we have first the Domain and then the Kingdoms of which right now seven exists (figure 2).

Figure 1: The hierarchy of biological classification’s eight major taxonomic ranks[1]

While we have now seven kingdoms for most of the time, there were only two – Animalia and Vegetabilia/Plantae (figure 2). The Kingdom of Fungi was first introduced in 1969 by Whittaker.

The separation of fungi from the rest of the plants was only possible due to more research. Especially within the domain eukaryotes, and the study of the cells led to the separation of fungi from plants[2].

This distinguishing has, to some extent, impacted how we as humans interact with fungi, especially regarding dietary norms or religions. But that is for another article.

Figure 2: Development of the kingdom-level classification over time[3]

Within the kingdom Fungi, we can find seven major phyla or groups (figure 3, Microsporidia not shown). This classification stems from the sexual reproductive structure of the fungi within each phyla..

Figure 3: Main groups of fungi[4]

What we call “mushrooms” falls in the phyla Basidiomycota (known as club fungi), and Ascomycota (known as sac fungi) both are part of the subkingdom Dikarya within the kingdom Fungi[5].

Within the group Basidiomycota which contains 31,515 species[6] we find mushrooms, puffballs, stinkhorns, bracket fungi, other polypores, jelly fungi, boletes, chanterelles, earth stars, smuts, bunts, rusts, mirror yeasts, and the human pathogenic yeast Cryptococcus[7].

Within the group Ascomycota, we will find over 64,000 species which are divided into three subphyla (class) Pezizomycotina (e.g., truffles, caterpillar fungus, cordyceps, morel), Saccharomycotina (e.g. “true” yeast), and Taphrinomycotina.

Which means what we call “mushrooms” is actually way more. “A mushroom [….] is the fleshy, spore-bearing fruiting body of a fungus, typically produced above the ground, on soil, or on its food source[8].” We, therefore, extend the name “mushroom” to similar fungi because of the deviation of their forms[9].

To make things more complicated, many fungi form a symbiosis with plants, algae and cyanobacteria, and insects. But they also act as pathogens and parasites[10]. In the world of the fungus, mycorrhiza is a symbiotic association with a plant[11].

This relationship consists of an exchange of sugar-water and minerals. While the fungus receives sugar (carbohydrates), the plants are provided with the necessary minerals[12]. These relationships are present in 92% of the plant families.

LIFE CYLCE

When it comes to the life cycle, we must distinguish between the life cycle of mushrooms (figure 4) and the life cycle of mycorrhiza (figure 5).

Mushroom

The part of a fungus that we usually call a mushroom is the fruiting body of a fungus. They are only built to spread spores. The building of the fruiting bodies only occurs if there are triggers that signal the fungus to initiate the process and get ready to reproduce.

Such triggers can be light, change in temperature, and or change in the CO2/O2 ratio.

Figure 4: Mushroom life cycle[13]

Mycorrhiza

In the case of mycorrhizae, the life cycle begins when fungal spore germinates, and hyphae grow toward a host root. The fungus then signals the host, and a change in the plant’s immune system occurs. After that, the fungus penetrates the host, and the symbiosis starts[14].

In the case of mycorrhizal fungus, the fungus cannot obtain carbon without them[15]. This means if the host dies, the fungus has to find another host to survive. As research showed, mycorrhizal fungi are continually searching for a new host while simultaneously engaging in symbiosis[16].

Figure 5: Life Cylce of a mycorrhizal fungus (AM fungi)[17]

Fungi which have a symbiotic relationship are for example truffles and morels.

If you are wondering if truffles can be cultivated. Then you should check out my article. In this article, I introduce you to the world of black gold and how truffles are been cultivated today in several countries.

DECOMPOSER

“Decomposers are organisms that break down dead or decaying organisms […][18]” In this decomposing process fungi play an important role[19]. They can break down organic matter (hemicellulose, cellulose, lignin). Some of these fungi developed the necessary enzyme to decompose lignin[20]. Because of that, they are called wood-decay fungi.

Some of them go after deadwood (brown rot), and some after living trees[21] (some white-rot). But all of them need water (> 28%) and oxygen to start the decomposing proces[22].

Wood-decay fungi are classified in three categories[23]:

  • Brown-rot
  • Soft-rot
  • White-rot

Each of them produces a different mixture of enzymes to break down plant materials. While brown-rot fungi can break down hemicellulose and cellulose, soft-rot fungi can only break down cellulose. Quite contrary to the white-rot fungi, which can break down lignin[24].

If we refer back to the taxonomy, only basidiomycetes can depolymerize and mineralize of lignin[25].

Common white-rot fungi are Shiitake, Oyster, and turkey tail[26] as well as Grifola frondosa[27].

But that is not all. Within the group of decomposers, we have to distinguish between primary, secondary, and tertiary decomposers. While primary decomposer lives off dead plants, secondary decomposers can only live off what the primary decomposer left over. Tertiary decomposers off that form the secondary decomposers.

According to that classification, we find in the group of primary decomposers Pleurotus, Shiitake, Nameko, or Ganoderma. While Agaricus is a secondary decomposer.

SUMMARY

Mushrooms are part of the kingdom Fungi, which plays an essential role in the ecosystem. In it, they form symbiosis or decompose wood. They, therefore, support many plants with minerals and helping to recycle organic matter.

Mushrooms are a world of its own!

If you want to know what kinds of mushrooms are currently grown or if you want to know what kinds of mushrooms you should grow, then you should check out my article about 26 Delicious Mushroom Species You Should Cultivate. In it, I will give you the main growing conditions as well as the regions where they are cultivated today.


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