Types of Fungi

A Classification System

Fungi are eukaryotic organisms, like plants and animals. Unlike plants, they don't perform photosynthesis and they have chitin, a derivative of glucose, in their cell walls. Like animals, fungi are heterotrophs, which means they get their nutrients by absorbing them.

Although most people think one difference between animals and fungi is that fungi are immobile, some fungi are motile. The real difference is that fungi contain a molecule called beta glucan, a type of fiber, in their cell walls.

While all fungi share some common characteristics, they can be broken into groups. However, scientists who study fungi (mycologists) disagree on the best taxonomic structure. A simple layman's classification is to divide them into mushrooms, yeast, and molds. Scientists tend to recognize seven subkingdoms or phyla of fungi.

In the past, fungi were classified according to their physiology, shape, and color. Modern systems rely on molecular genetics and reproductive strategies to group them. Keep in mind that the following phyla aren't set in stone. Mycologists even disagree about the names of species

Subkingdom Dikarya: Ascomycota and Basidiomycota

Penicillium notatum is a fungus belonging to the phylum Ascomycota.
Penicillium notatum is a fungus belonging to the phylum Ascomycota. ANDREW MCCLENAGHAN/SCIENCE PHOTO LIBRARY / Getty Images

The most familiar fungi probably belong to the subkingdom Dikarya, which includes all mushrooms, most pathogens, yeast, and molds. Subkingdom Dikarya is broken into two phyla, Ascomycota and Basidiomycota. These phyla and the other five that have been proposed are differentiated based mainly on sexual reproductive structures.

Phylum Ascomycota

The largest phylum of fungi is Ascomycota. These fungi are called ascomycetes, or sac fungi, because their meiotic spores (ascospores) are found in a sac called an ascus. This phylum includes unicellular yeasts, lichens, molds, truffles, numerous filamentous fungi, and a few mushrooms. This phylum contributes fungi used to make beer, bread, cheese, and medicines. Examples include Aspergillus and Penicillium.

Phylum Basidiomycota

The club fungi, or basidiomycetes, belonging to the phylum Basidiomycota produce basidiospores on club-shaped structures called basidia. The phylum includes most common mushrooms, smut fungi, and rust. Many grain pathogens belong to this phylum. Cryptococcus neoformans is an opportunistic human parasite. Ustilago maydis is a maize pathogen.

Phylum Chytridiomycota

Chytridiomycosis is believed to affect about 30% of amphibians worldwide, contributing to the global decline in populations.
Chytridiomycosis is believed to affect about 30% of amphibians worldwide, contributing to the global decline in populations. Quynn Tidwell / EyeEm / Getty Images

Fungi belonging to the phylum Chytridiomycota are called chytrids. They are one of the few groups of fungi with active motility, producing spores that move using a single flagellum. Chytrids get nutrients by degrading chitin and keratin. Some are parasitic. Examples include Batrachochytrium dendobatidis, which causes an infectious disease called chytridiomycosis in amphibians.

Reference: Stuart, S. N.; Chanson J. S.; et al. (2004). "Status and trends of amphibian declines and extinctions worldwide." Science. 306 (5702): 1783–1786.

Phylum Blastocladiomycota

Corn is subject to numerous fungal infections. Physoderma maydis causes brown spot disease.
Corn is subject to numerous fungal infections. Physoderma maydis causes brown spot disease. Edwin Remsberg / Getty Images

Members of the phylum Blastocladiomycota are close relatives to the chytrids. In fact, they were considered to belong to the phylum before molecular data led them to become separate. Blastocladiomycetes are saprotrophs that feed on decomposing organic material, such as pollen and chitin. Some are parasites of other eukaryotes. While the chytrids are capable of zygotic meiosis, the blastocladiomycetes perform sporic meiosis. Members of the phylum display alternation of generations.

Examples are Allomyces macrogynus, Blastocladiella emersonii, and Physoderma maydis.

Phylum Glomeromycota

The hyphae of the black bread mold are the threadlike structures. The round structures are called sporangia.
The hyphae of the black bread mold are the threadlike structures. The round structures are called sporangia. Ed Reschke / Getty Images

All fungi belonging to the phylum Glomeromycota reproduce asexually. These organisms form a symbiotic relationship with plants where the hyphae of the fungus interact with plant root cells. The relationships allow the plant and fungus to received more nutrients.

A good example of this phylum is black bread mold, Rhizopus stolonifer.

Phylum Microsporidia

Microsporidiosis is an intestinal infection that causes diarrhea and wasting. It mainly affects immunocompromised individuals.
Microsporidiosis is an intestinal infection that causes diarrhea and wasting. It mainly affects immunocompromised individuals. PhotoAlto/Odilon Dimier / Getty Images

The phylum Microsporidia contains fungi that are spore-forming unicellular parasites. These parasites infect animals and protists, a unicellular organism. In humans, the infection is called microsporidiosis. The fungi reproduce in the host cell and release cells. Unlike most eukaryotic cells, microsporidia lack mitochondria. Energy is produced in structures called mitosomes. Microsporidia are not motile.

An example is Fibillanosema crangonysis.

Phylum Neocallimastigomycota

Cattle and other ruminants rely on fungi from Neocallimastigomycetes to digest cellulose fiber.
Cattle and other ruminants rely on fungi from Neocallimastigomycetes to digest cellulose fiber. Ingram Publishing / Getty Images

The Neocallimastigomycetes belong to the phylum Neocallimastigomycota, a small phylum of anaerobic fungi. These organisms lack mitochondria. Instead, their cells contain hydrogenosomes. They form motile zoospores that have one or more flagellae. These fungi are found in cellulose-rich environments, such as the digestive systems of herbivores or in landfills. They have also been found in humans. In ruminants, the fungi play an essential role in digesting fiber.

An example is Neocallimastix frontalis.

Organisms That Resemble Fungi

Slime molds look like fungi, but lack fungal characteristics at the cellular level.
Slime molds look like fungi, but lack fungal characteristics at the cellular level. John Jeffery (JJ) / Getty Images

Other organisms look and act much like fungi yet are not members of the kingdom. Slime molds are not considered fungi because they don't always have a cell wall and because they ingest nutrients rather than absorb them. Water molds and hyphochytrids are other organisms that look like fungi yet are no longer classified with them.