 Synonyms may arise whenever the same taxon is described and named more than once, independently.They may also arise when existing taxa are changed, as when two taxa are joined to become one, a species is moved to a different genus, a variety is moved to a different species, etc.Synonyms also come about when the codes of nomenclature change, so that older names are no longer acceptable; for example, "Erica herbacea" L. has been rejected in favour of "Erica carnea" L. and is thus its synonym.