Our planet is a dynamic system that is home to an unthinkable number of living organisms.
Within the vast expanse of diverse life on Earth, where do fungi fall into place? There are
more than 120,000 species of fungi that have been classified by mycologists. In order to understand
how they make sense of all of these species, it is essential to understand the modern system of
biological classification called taxonomy. We have covered this in some detail in the biology series,
so be sure to check out that tutorial if it sounds unfamiliar. Otherwise, to briefly review,
there are generally eight or more levels that go into classifying an organism. In the direction of
increasing specificity, these are domain, kingdom, phylum, class, order, family, genus, and species,
and we refer to each of these levels as a taxon. Let’s work our way down these taxa in order to
classify a particularly notorious mushroom, the fly agaric, or Amanita muscaria. So let’s start
by zooming out as far as possible, considering the totality of all the living organisms on the
planet. The broadest category of classification is a domain. There are three of these, which are
Bacteria, Archaea, and Eukarya. All fungi have nucleated cells, and therefore are eukaryotes,
in contrast with the other two domains, which contain unicellular prokaryotic organisms.
Thus, fungi fall into the Eukarya domain. Plants and animals are also eukaryotes, and there is a
common misconception that plants and fungi are highly related in the tree of life. However,
fungi are actually more related to animals than plants. So, scientists have classified
animals and fungi in their own taxonomic lineage called opisthokonts. Within the opisthokonts,
we can reach the next level of classification, and that is the kingdom which is encompassed by
this series, the Fungi kingdom. Any organism within this kingdom is considered a fungus.
Now from here, mycologists use structural patterns and genetic factors to classify
each fungal species into their respective taxa. The taxon below the kingdom is called the phylum.
The precise number of fungal phyla and their names has changed quite a bit over the past few decades,
as mycology is a young and dynamic field, and there are some differing opinions as to which
groups should qualify as phyla and which should be referred to merely as subphyla. In general,
phyla will have the suffix “mycota” and subphyla will have the suffix “mycotina”,
and in this series we will consider eight fungal phyla. These are Basidiomycota, Ascomycota,
Chytridiomycota, Blastocladiomycota, Mucoromycota, Zoopagomycota, Glomeromycota, and Cryptomycota.
There are individual characteristics within each of these phyla that allow us to differentiate
between them, and we will discuss these as we move through the series. The Chytridiomycota,
Blastocladiomycota, and Cryptomycota contain all the zoosporic fungi,
or single-celled fungi which possess a flagellum at some point during their life cycles.
The phyla Mucoromycota, Zoopagomycota, and Glomeromycota contain fungi which
have lost the flagellum but have developed the ability to grow with filamentous hyphae.
Finally, and most notably, the two phyla Basidiomycota and Ascomycota are often
grouped together as the subkingdom Dikarya, also known as the higher fungi. This name
refers to the pair of nuclei in the hyphae of a mycelium which has DNA from two individual fungi,
and they are known as the higher fungi because these phyla produce the macroscopic mushrooms
that you can see with the naked eye. So, most of the well-known fungi fall into the Dikarya
subkingdom. As it is a multicellular fungus, the fly agaric falls into the subkingdom Dikarya
and, more specifically, is placed into the phylum Basidiomycota. The main difference between
mushrooms within the Basidiomycota and Ascomycota are the spore-producing structures, or hymenium,
on their respective sporocarps or fruiting bodies. The sporocarps from the phylum Ascomycota are
known as ascocarps and from Basidiomycota, they are known as basidiocarps. The ascocarps produce
sacs of spores called asci and are therefore commonly known as sac fungi. The basidiocarps
form club-like structures that produce spores called basidia and are therefore commonly known as
club fungi. The fly agaric is a club fungus, so we classify it further into the phylum Basidiomycota.
The taxon below a phylum is known as a class. Any class within the kingdom of fungi has the ending
“mycete”. There are three subphyla within the phylum Basidiomycota, and within each of these,
there are numerous classes. As we go down each taxon, the amount of specificity to classify
needs to increase, which leads to innumerable divisions. We do not have time to cover each
of these divisions in this tutorial, though many of them will be discussed as we move through the
series. Regardless, we need to finish classifying our fly agaric, Amanita muscaria. This falls into
the class Agaricomycetes and then is part of the order Agaricales. Any order will have the ending
“ales”. Generally, the order Agaricales describes any mushroom with gills or lamellae.
Within the order, the fly agaric is further classified into the Amanitaceae family. Whenever
the taxon name ends with “aceae”, that name describes a taxonomic family. Knowing the family,
we finally can reach the genus Amanita, and after that, the species muscaria. Just as when writing
the official name of any other organism, for this fungus we include both the mushroom’s genus and
species, italicizing both taxa, and capitalizing only the genus. This naming scheme is known as
binomial nomenclature. So, the full scientific name of the fly agaric is Amanita muscaria.
Any other mushroom will be classified just as we did with Amanita muscaria. Each division down the
tree of life reveals the fundamental nature and properties of every studied organism. Within the
kingdom of fungi, there are still millions of species that have yet to be classified.
Only with the help of professional and amateur mycologists can we further this
endeavor. Mycology still has so many mysteries within its branch on the ever-expanding tree of
life. Let’s keep moving forward, so that we may gather the ability to unravel those mysteries.