Each species, which is considered to be distinct from other related organisms, has a unique Latin name that consists of 2 parts (called a binomial): the genus name and the species name. There might also be a subspecies name, resulting in a trinomial. The spelling of Latin binomials and trinomials should be checked (see the subsections on plants, animals and so on for authoritative sources).
Caution! Note that different rules apply when referring to bacterial serovars; see Bacterial names. Virus names also follow different rules; see Virus names.
Use italics for genus, species and subspecies names, with an initial capital for the genus name and lower case for the species and subspecies names; the rank of a trinomial is in roman:
Mus musculus Eucalyptus globulus Eucalyptus globulus var. bicostata Salmonella enterica Homo sapiens sapiens
Species names are always singular:
Cyathodes platystoma is restricted to wet eucalypt forests not Cyathodes platystoma are restricted to wet eucalypt forests
as are genus names:
Cyathodes is endemic to Tasmania.
Do not use commas when the name is defining:
The species Eucalyptus globulus is the only member of the genus that ... not The species, Eucalyptus globulus, is the only member of the genus that ...
Abbreviating the genus name
After the genus and species names have been given in full at the first mention, the genus name can be abbreviated to the first letter followed by a full stop. Include a space between the stop and the species name; use a nonbreaking space to avoid the name splitting over a line:
How to insert a nonbreaking space:
Use Ctrl+Shift+Space (Windows), or Option+Space (Mac).
Did you know? A nonbreaking space appears in the text like a ‘degree’ symbol: °.
Ensure that there is no confusion with other names in use in the text:
The gram-positive bacterium Streptococcus pyogenes causes rheumatic fever. Recently, scientists in the United States sequenced the S. pyogenes genome.
The biting midge Culicoides brevitarsis is the main vector of 2 viruses in Australia ... The vector is believed to be the mosquito Culex annulirostris. This mosquito is less susceptible to climatic extremes than C. brevitarsis and often has a wider distribution.
[There is no ambiguity about which genus the C. in C. brevitarsis is referring to.]
Specimens from a range of taxa were collected, including Olearia hookeri, Ozothamnus hookeri, Monotoca glauca and Trochocarpa disticha. Of these species, only Ozothamnus hookeri is found in montane habitats. Olearia hookeri occurs in dry areas of the east coast, and M. glauca and T. disticha are wet forest species.
[The generic names Olearia and Ozothamnus need to be put in full because O. hookeri could refer to either genus.]
Do not use abbreviations comprising 2 or more letter to distinguish genera with the same initial (eg St and Sa for Streptococcus and Salmonella, respectively), because these abbreviations are not standardised, and such use can lead to inconsistencies between documents. If there is any confusion, write out the genus name in full at each mention.
The styles of some journals and organisations allow a genus name to be abbreviated at the beginning of a paragraph or sentence, whereas others do not, so check the house style that you are writing or editing for.
Give the genus name in full the first time it appears in the title of a table, in the text of table, and in the caption of a figure or photograph.
Referring to unnamed or multiple species in a genus
Use ‘sp.’ when referring to a single species from a genus when the species name is unknown, uncertain or unnamed:
A new species (Grevillea sp.) was discovered in the national park.
Use ‘spp.’ when referring to multiple species in a genus:
Many tree species (Eucalyptus spp. and Acacia spp.) regenerated after the fires.
Note that ‘sp.’ and ‘spp.’ are not set in italics.
When referring to the genus as a whole, use the genus name alone:
Culicoides biting midges are known to be vectors of various diseases not Culicoides spp. biting midges …
A genus name does not have a plural form (but see Common names derived from family and genus names for plurals of genus names used as common names):
Grevillea spp. not Grevilleas
Describing actions involving specific plants and animals
Latin binomial species names are abstract concepts and therefore cannot be used as the subject of a direct action. In this case, use the common name of the plant or animal concerned:
Tobacco plants (Nicotiana tabacum) have been inoculated ... not Nicotiana tabacum has been inoculated ... [ie the plant is inoculated, not the taxon]
Mice (Mus musculus) were fed a diet containing … not Mus musculus were fed …