Genus is a principal taxonomic category in organizing biological classification. It represents a collection of related species; a collection of related genera are grouped into a family. The rules surrounding the application and usage of taxonomic labels is highly formalized, and often confusing; below are some notes that I have collected for my own use when noding Earthly flora and fauna.
In modern convention, the genus name is always capitalized, while the species name never is; both are always either italicized or underlined; italicization is more common. A proper form should look like this: Genus species.
While technically only the second part of the Latin name is species specific, a species should always be referred to by both genus and species name; this is called the full specific name.
Every genus name is unique; this is not true of species names (hence we have Phaseolus vulgaris, Beta vulgaris, and Sciurus vulgaris, among dozens of other vulgarrises, but only one group with the name Phaseolus).
Taxonomic levels higher than genus are not italicized, but are capitalized.
The plural of genus is genera.
Brevity Quest 2016