As convenções são as seguintes (Extraído de International Code of Nomenclature for algae, fungi, and plants - Melbourne Code):

3.1. The principal ranks of taxa in descending sequence are: kingdom (regnum), division or phylum (divisio or phylum), class (classis), order (ordo), family (familia), genus (genus), and species (species). Thus, each species is assignable to a genus, each genus to a family, etc.

4.1. The secondary ranks of taxa in descending sequence are tribe (tribus) between family and genus, section (sectio) and series (series) between genus and species, and variety (varietas) and form (forma) below species.
4.2. If a greater number of ranks of taxa is desired, the terms for these are made by adding the prefix “sub-” to the terms denoting the principal or secondary ranks. An organism may thus be assigned to taxa of the following ranks (in descending sequence): kingdom (regnum), subkingdom (subregnum), division or phylum (divisio or phylum), subdivision or subphylum (subdivisio or subphylum), class (classis), subclass (subclassis), order (ordo), suborder (subordo), family (familia), subfamily (subfamilia), tribe (tribus), subtribe (subtribus), genus (genus), subgenus (subgenus), section (sectio), subsection (subsectio), series (series), subseries (subseries), species (species), subspecies (subspecies), variety (varietas), subvariety (subvarietas), form (forma), and subform (subforma).

O Reino é a categoria superior da classificação científica dos organismos introduzida por Lineu no século XVIII.

Referência

Ruggiero MA, Gordon DP, Orrell TM, Bailly N, Bourgoin T, Brusca RC, et al. (2015) A Higher Level Classification of All Living Organisms. PLoS ONE 10(4): e0119248. doi:10.1371/journal.pone.0119248