Kingdom Fungi

Kingdom fungi is responsible for decomposing and recycling organic matter back into the environment as nutrients. Nearly 150,000 species of fungi are classified, yet millions are estimated to exist.

The majority of the mushrooms large enough to see with the naked eye are in the subkingdom Dikarya. They are known as higher fungi and come in all shapes and sizes. However, not all fungi are the typical multicellular mushrooms you see at the grocery store. Some like yeast are microscopic and unicellular. Below you'll find a list of the common groups of fungi. The groups are not the scientific classifications, but an easy way to categorize similar species.

  • Gilled Mushrooms
  • Puffballs
  • Stinkhorns
  • Bracket fungi
  • Polypores
  • Jelly fungi
  • Boletes
  • Corals
  • Crusts
  • Chantrelles
  • Earthstars
  • Smuts
  • Bunts
  • Rusts
  • Cup Fungi
  • Yeasts
  • Morels
  • Truffles
  • Earth Tounges
  • Lichen

A common misconception is to think that the mushroom is the primary structure of a fungus. However, the mushroom is only the reproductive structure or fruiting body. The mycelium is the vegetative body (thallus) of fungi. It consists of a network-like mass of thread-like filaments called hyphae. A hypha is an individual cell that repeatedly branches out in search of nutrients. The cell walls of hyphae comprise of chitin, a strong fibrous substance. When the hyphae find a food source, they secrete enzymes to digest the organic matter externally. The tips of the hyphae then absorb the nutrients. There are two types of hyphae, septate hyphae, and aseptate hyphae.

  • Septate hyphae have cross-walls called septa (singular: septum) that divide each cell. Nutrients, cytoplasm, and organelles can flow between cells by a pore located on a septum.
  • Aseptate hyphae do not contain cross-walls which allows for nutrients, cytoplasm, organelles, and large amounts of nuclei to flow freely.

Ecology of Fungi

Fungi have colonized our planet. They can thrive in nearly every environment from forests, oceans, tundras, and even inside other living beings. The air we breathe is also full of fungal spores. Typically fungi prefer cool, dark, and damp habitats. There are three unique relationships fungi share with their environment.

Saprotrophic Fungi

Saprophytic fungi or saprobes feed on dead organic material, debris, or waste. They recycle their food into beneficial nutrients like nitrogen and phosphorus. Our forest would be covered in fallen debris if not for saprobes that consume leaves, branches, stumps, and even deceased animals.

Mutualistic Fungi

Some fungi maintain a symbiotic relationship with other organisms. Both species will benefit from this relationship. The host typically contributes carbohydrates in exchange for nutrients and water provided by the fungi.

Mycorrhizal Fungi

Mycorrhizae have a unique bond with a plant's root system. For that reason, it makes cultivating some species nearly impossible. Mycorrhizal fungi include morels, truffles, chanterelles, porcini, matsutake, and more.

  • Ectomycorrhiza: Mycelium envelops the roots of the host plant but does not penetrate their cell walls.
  • Endomycorrhiza: Mycelium penetrates the cell wall of the host plant without harming it. Most Endomycorrhiza fungi do not produce fruiting bodies.

Lichen

Lichen is the result of a mutualistic relation between fungi and algae. In their union, the algae will use photosynthesis to provide energy while the fungus gathers water and nutrients. Only light, air, and minerals are needed for lichen to survive, which allows them to grow in harsh environments.

Parasitic Fungi

Parasitic fungi benefit while harming their host. Specialized hyphae called haustoria will grow within the host's tissue, absorbing nutrients. The host will be weakened or die because of the fungi. Athlete's foot, candida, and ringworm are a few examples of parasitic fungi in humans.

Many plant diseases are a result of pathogenic fungi such as brown or white rot. Smuts and rusts also cause widespread damage to the yields of important cash crops.

Cordyceps are parasitic fungi that infect insects. The fungus penetrates the chitin exoskeleton of insects and slowly begins to zombify the host. Once the fungus is ready to fruit, it will control the insect to climb to a high vantage point to maximize spore dispersal.

Domain Eukaryote

Like animals and plants, Kingdom Fungi belongs to the domain eukaryote. Meaning their cells contain membrane-bound nuclei and organelles. It is a common mistake to assume that mushrooms are plants, but fungi are more related to animals.

Kingdom Plantae

Plants and fungi are immobile and have a sort of root-like structure. However, species within kingdom Plantae are all multicellular organisms with a cell wall made of cellulose. They also contain chloroplasts allowing them to obtain energy through photosynthesis. While most plants are autotrophs, some species are heterotrophic. In contrast, fungi get energy through consuming organic matter, and chitin comprises their cell walls.

Kingdom Animalia

Both animals and fungi are heterotrophs; they store carbohydrates as glycogen; and require food, water, and oxygen to live. However, the two kingdoms differ in many ways. Mobility is a distinct difference, as fungi are immobile. Animals digest food internally; in contrast, fungi digest their food externally by secreting enzymes on organic matter and absorbing the necessary nutrients. The cell walls are not present in animals, but some like insects and crustaceans create chitin for their exoskeletons.

Taxonomy: Scientific Classification

Kingdom Fungi branches off into subkingdoms and divisions. Traditionally fungi are classified by the way they reproduce. Modern-day genetic sequencing is rapidly advancing taxonomic classifications. The dramatic reorganization of taxa is the root cause of much confusion. Many books and online resources are out-of-date, resulting in conflicting information. My goal is to deliver this information as coherent and accurate as possible.

Divisions of Kingdom Fungi

Basidiomycota Division

Also known as club-fungi consisting of around 50,000 species.

Basidiomycota

Ascomycota Division

Also known as cup-fungi consisting of around 90,000 species.

Ascomycota

Chytridiomycota Division

Also known as chytrids, consisting of around 980 species. Most fungi are aquatic and produce flagellated spores.

Mucoromycota Division

A newer division consisting of around 760 species of molds.

Zoopagomycota Division

A newer division consisting of around 900 species.

Blastocladiomycota Division

A newer division consisting of around 220 species.

Cryptomycota Division

A newer division consisting of around 30 species.

Microsporidia Division

A newer division consisting of around 1,250 species.

Depreciated Divisions

Two divisions no longer exist because of the reclassification. They are listed in many resources, but they are currently broken up into more logical taxa.

Zygomycota

The fungi in the depreciated division Zygomycota consisted of common molds. Also known as zygomycetes, they were multicellular fungi that reproduced both sexually and asexually. The majority of the species were terrestrial and formed a mutualistic relationship with plants. The species were divided into two new divisions: Mucoromycota and Zoopagomycota.

Deuteromycota

The depreciated division Deuteromycota could be considered the junk drawer of fungi. The division was known as imperfect fungi and a catch-all for diverse species without an observed sexual stage.

Phylum vs. Division?

In the biological classification (taxonomy) of organisms, both "phylum" and "division" are used, though they are utilized differently in botany and zoology.

In the context of zoology, animals are grouped into various phyla (plural of phylum). For example, Arthropoda (which includes insects, spiders, and crustaceans), Mollusca (which includes snails, clams, and squids), and Chordata (which includes vertebrates like humans, birds, and fish) are all phyla.

However, in botany, which traditionally includes the study of fungi along with plants, the term "division" has been used in place of "phylum". For instance, fungi are classified into divisions such as Ascomycota and Basidiomycota.

The difference in terminology is largely historical and relates to the separate development of zoological and botanical nomenclature. In more recent years, there has been a trend toward uniformity, and "phylum" is being used more consistently across both zoological and botanical classifications. This shift is in part due to the influence of the PhyloCode, a developing system of phylogenetic nomenclature that seeks to regulate the naming of clades.

So, while you might see both terms used, especially in older sources, current practice tends towards using "phylum" even for fungi.

Winner: Phylum