What's in a Name?
A scientific name has two parts: the genus name, and the species epithet. Equus is the genus name for horses and their close relatives. There can be many species in a genus. Another species in the genus Equus is Equus burchellii, the plains zebra of Africa. The species epithet burchellii, combined with the genus name Equus sets the zebra apart from the horse.
The system of scientific names is an information system that organizes life forms into groups, based on their biological and evolutionary relationships. The largest of these groups is called a "kingdom". There are five kingdoms, one of which is the Fungi. Within the Fungi, as in all the kingdoms, the members are organized into ascending ranks. Closely related species are grouped into the rank of genus.
Because "systematic" groups are based on biological and evolutionary relationships, all members of a group are similar to one another. For example, all species in the fungus genus Puccinia are plant rusts, a kind of parasite which grows on live plants. Genera are grouped into families, whose members may show more variety, but are basically the same kind of organism. The genus Puccinia is placed in the family Pucciniaceae. All the genera in the family Pucciniaceae are plant parasites.
Is it mold or mildew in that basement corner? Is the bright umbrella-shaped fungus you have found beneath a tree a mushroom or a toadstool? Have you ever seen a horse wearing a Dryad's Saddle, or spread your morning toast with Witch's Butter? All the above terms, like toadstool, are common names. Common names are given to organisms in the language of the people who live with them. For example, "horse", "cheval", "el caballo" and "pferd" are all common names for the organism with the scientific name Equus caballus . In some countries, if a horse possesses white patches on a darker coat, it can also be called by the name of "Pinto". Its scientific name will still be Equus caballus, because a Pinto's unique color does not make it a different animal from any other Equus caballus. In horses, color is not a "diagnostic characteristic".
Diagnostic characteristics are those features that make one particular species unique from all other species. While an organism can have common names in many languages, it possesses only one scientific name, in Latin. This name is unique, only being used once in science to describe an organism.
Scientists carefully research and study the relationships between fungi and other forms of life in order to understand them and assign scientific names based on their understanding. Why do they work so hard, when the people who live with the organisms have already given them common names? Why have both?
Why Have Both?
First, not all organisms have a common name. In the Fungi, many species live in the soil and escape notice in everyday life. Others are not edible, or, at this time, not economically important, and are ignored. These fungi will probably never receive common names, though they all have scientific names. This name duplication cannot happen with scientific names. Their unique status is enforced by the International Code of Botanical Nomenclature's rules for creating a single "valid name". The procedure includes publishing a Latin description of the organism.
With fungi, as with all organisms, common names can borrow from mythology or local history, and are often descriptive of the physical properties of a fungus. The fungus genus name Geastrum is a combination of the Latin Ge, meaning "earth" and astrum, meaning "star". The common name used for all the species in this genus is "earthstar."
Although unique, a scientific name may change. As improved methods of research provide scientists with more information on a species' evolutionary relationships, their scientific name is sometimes changed to reflect this better understanding. The fungus may be placed in a different genus, or family. The change from evaluating fungi with the naked eye to the use of a microscope to examine spores was one improvement in research that resulted in name changes. More recently, the assignment of names that accurately reflect biological relationships has been helped by the highly detailed spore images that result from scanning electron microscopy (SEM), and DNA analysis.