The rules by which botanical infraspecific taxa are named specify that the name shall consist of the name of the parent species followed by a term which denotes the rank of the subdivision, and an epithet which is formed in the same ways as specific epithets, including grammatical agreement when adjectival. Such names are subject to the rules of priority and typification. The ranks concerned are subspecies (abbreviated to subsp. or ssp.), varietas (variety in English, abbreviated to var.), subvarietas (subvariety or subvar.), forma (form or f.). These form a hierarchy, and further subdivisions are permitted, but the Code does not define the characteristics of any rank within the hierarchy. Consequently, infraspecific classification is subjective.