Article 4. Names of taxa at ranks above the species group
The scientific name of a taxon of higher rank than the species group consists of one word (i.e. the name is uninominal); it must begin with an upper-case letter [Art. 28].
The scientific name of a subgenus must not be used as the first name in a binomen or trinomen unless it is being used at the rank of genus [Art. 6.1].