Taxon represents a taxonomic hierarchy (from family through species). This
class represents a number of validity checks to ensure the taxon is correctly
structured. A taxon must have at least a family specified, and neither genus
nor species can be specified without the "shallower" layers of the hierarchy
specified first. Group Taxons together with Taxa().
Usage
Taxon(family = NA_character_, genus = NA_character_, species = NA_character_)