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The classification hierarchy

species names and identification

There are different degrees of relatedness in the living world. For example, probably everyone knows that Labradors, Border Collies and wolves are related (all being "dogs" in a broad sense) but that Labradors are more closely related to Border Collies than they are to wolves. Examples of other animals in the broad "dog" group are the dingo, coyote, jackal, the various foxes, the Cape hunting dog of Africa and the Indian bush dog. Similarly there's some unifying quality that puts creatures as varied as bees, butterflies, cicadas, cockroaches and silverfish into one large group called the insects. Finally, "dogs" and insects are part of a very large group - the animals.

The varying degrees of relatedness lead to the concept of a hierarchy of different levels of classification and there are particular terms to denote the different levels in the hierarchy. Individuals that are very closely related are grouped into the one species. Related species are grouped into a genus (plural: genera). Related genera are grouped into a family and, going to still broader groupings (or higher levels of classification), there are orders, classes, divisions (also called phyla, with phylum the singular) and finally kingdoms.

Sometimes categories finer than species are used, and there can be various categories that are intermediate between the levels that have just been given in bold, for example, subclass (which lies between order and class). However, while they are relevant to a specialist, they will be ignored here since they merely introduce technical complexities but illustrate no additional classificatory principles.

While there are many visible differences between the breeds of domesticated dogs, they are all in the one species – with the scientific name Canis familiaris (using two Latin words: canis = dog and familiaris = intimate or friendly). The dingo and the wolves are related to domestic dogs, but not closely enough to be placed in the same species. However, the relationship is close enough to have them both in the same genus, Canis.

Elsewhere on this website, you've probably already seen the two-part scientific names for many fungal species and you've just seen the species name for domesticated dogs – Canis familiaris.

The species epithet indicates a particular subgroup of the genus.

The foxes are more distantly related to domestic dogs and are placed in different genera. For example, the European red fox is placed in genus Vulpes. The broad "dog" group, explained above, makes up the family Canidae.

The insects constitute a Class, technically called the Insecta and the animals constitute a Kingdom – Animalia.

Given the explanation of species, genus, etc that was given above, it’s clear that there are fewer genera than there are species, fewer families than there are genera, and so on. However, there's a greater diversity of organisms in a genus than in a species, a still greater diversity in a family and so on. For example, while Family Canidae consists of all the "doggy" animals, going a step up from that Family you get the Order Carnivora, which contains the "dogs" and all the other meat-eating, placental mammals – animals as varied as cats and seals.

The genus epithet always starts with a capital letter and the two-part species name is always written in a way different to the rest of the text – commonly in italics. These are simply conventions. In the great majority of cases, the classification of an organism stops with species and only the genus epithet and species epithet are used to make up the scientific name. In cases where finer levels than species have also been used in the classification, those finer level terms would also be used in the scientific name. However, as before, such technical niceties will be ignored here.

You’ve already seen that a particular genus epithet can turn up in many species names. Getting back to fungi, here are three examples: Amanita muscaria , Amanita phalloides and Amanita xanthocephala .

Similarly, a particular species epithet can turn up in many species names. Here are two examples: Cortinarius archeri <<039>> and Anthurus archeri . <<074>>

Cortinarius archeri Different fungi - same specific epithet

Anthurus archeri

BUT.......

While there’s a relatively close relationship between two organisms with the same genus epithet, a common species epithet gives no information about the relationship. The only connection between the above two species with the species epithet archeri, is that they were both named in honour of the 19^th century Tasmanian botanist William Archer. Here are the classifications of the two species. The lowest level they have in common is Class, indicating a very distant relationship between the two.

In everyday terms, to identify somebody, it’s not enough to know that they’re in, say, the Fredericks family. Knowing that someone’s a member of the Fredericks family gives you some information about them - but it doesn’t identify them. You want to know if it’s Alan Fredericks or Sarah Fredericks. Similarly, knowing that the purplish mushroom pictured above is in the family Cortinariaceae would give you some information about its relationships to other fungi - but you can't say you've identified it until you've found the correct, two-part species name.

Cymatoderma elegans var. lamellatum

In most cases that means the two-part species name but, as explained earlier, sometimes you need to go to levels below species. For example, consider the funnel-shaped fruiting body shown in the accompanying photo. A number of mycologists consider that, amongst the organisms classed within the species Cymatoderma elegans, there are a number of easily distinguishable varieties. However, while the varieties differ from each other, the differences aren't considered significant enough to warrant creating a different species for each. Thus, they are called "varieties" within the species and the name for the pictured specimen is Cymatoderma elegans var. lamellatum, "var." being the abbreviation for "variety" (and you'll notice that "var." is not italicized). Variety is one of the levels finer than species. There are few (macro) fungi for which levels finer than species are used.

Different people can hold different ideas about classification. For example, two mycologists may disagree about the definition of a particular order or have different views as to which family a particular genus belongs. There is still much to be learnt about the relationships between the different fungi and while there is universal agreement about many aspects of fungal classification, there are also many areas in which the evidence is ambiguous. Understandably, if the evidence is ambiguous, different people will interpret it differently and the resolution of such ambiguity must rely on future research to unearth conclusive evidence for one of the conflicting views - or perhaps the evidence will show that all current views are wrong!

The classification scheme (or schemes) existing at any given time depend on the state of knowledge at that time. As knowledge increases, classification schemes change. Sometimes this leads to changes in the names of species, but often the change is at higher levels (such as the realization that Family X, once placed in Order A, should really be placed within Order B), with the name remaining unchanged.

Agaricus nidiformis 1844 Pleurotus nidfiformis 1887 Omphalotus nidiformis 1994 - current name

For example, the fungus pictured here, was first described in 1844 and given the name Agaricus nidiformis. An 1887 publication changed the name to Pleurotus nidfiformis and since 1994 it has been known as Omphalotus nidiformis. These changes in the genus part of the name reflect changing insights into the relationships between this luminous fungus and other fungi.

Sometimes a person may change his or her views. Going back to Cymatoderma elegans var. lamellatum, shown a little earlier, the mycologist who created this three-part name had previously named the same fungus Cymatoderma lamellata. Initially he would have thought its features warranted a separate species for the fungus, but later reconsidered his ideas and come to the conclusion that a separate species was unwarranted and so "reduced" the species Cymatoderma lamellata to simply a variety of another species, Cymatoderma elegans.

While there may be disputes over classification (or changes in someone's ideas), the procedures to be followed when naming fungi are governed by a set of rules, called the International Code of Botanical Nomenclature (ICBN). Everyone, regardless of their views on classification, will follow these procedures when it comes to naming a new species, changing the name of an existing species, defining a new genus and so on. Since botany is the study of plants and fungi are not included in the plant kingdom, why are the naming rules for fungi called the International Code for Botanical Nomenclature? Historical reasons. For a long time fungi were included in the plant kingdom. The ICBN covers the plant kingdom and those other organisms (such as fungi) that were once included in the plant kingdom.

Finally, why are the scientific names in Latin? The reason is largely historic, for Latin was the language of science in the 1700s and into the 1800s when the current system of scientific naming came into existence, and a great many scientific names were created in those years. By the time Latin lost its role as the common scientific language, it would have caused catastrophic confusion to change every name. Moreover, which living language should you use? You're bound to offend many people, no matter which living language you choose!

Though Latin is a dead language new words are often introduced from various non-Latin languages, "Latinized" and then used in scientific names. So, rather than Latin, you could call it pseudo-Latin. For example, the animal pictured here is well-known as the Common Wombat and the word "wombat" comes from an Australian aboriginal language. The scientific name of this species is Vombatus ursinus, the genus name being a Latinized version of "wombat". There are a number of Australian fungi with species epithets derived from aboriginal languages. To give just a few examples, from the genus Cortinarius: Cortinarius bambrus, Cortinarius kilpanius, Cortinarius kiambramemsis and Cortinarius yerillus.