(ICBN) A periodically revised publication outlining the procedures for the scientific naming of plants (i.e. vascular plants, bryophytes, algae, blue-green algae, fungi, and slime moulds). The rules have been drawn up to sort out errors and ambiguities arising from past misunderstandings and misidentifications and to ensure correct naming of new taxa. Fundamental to the code are the principles that naming of families and lower ranks is by reference to nomenclatural *types
, that the first valid name published is maintained (for vascular plants this is the first name published on or after 1 May, 1753, the date Linnaeus' Species Plantarum was published), and that once the circumscription, position, and rank of a group have been decided it can only have one correct name. However this does not preclude a group of plants being treated in different ways (e.g. being given a different position) by different authors, with each author being able to assign a different nomenclaturally correct name. For example, watercress is thought by some authors to belong to the genus Nasturtium, while others believe it is better placed in Rorippa. Following the rules of the Code, the names Nasturtium officinale and Rorippa nasturtium-aquaticum are equally acceptable. Names cannot be changed simply because they are inappropriate. However *homonyms
and superfluous names (names published for a taxon after that taxon already had a valid name) must be rejected. If two or more taxa are combined into one then the new taxon takes the name of the constituent that had the oldest valid name. If a taxon is split into two or more taxa, then one of the new taxa must be given the name of the old taxon.
The ICBN is only applicable to wild plants and because of the importance of many cultivated plants, a separate set of rules has been laid down in 57 Articles in the International Code of Nomenclature of Cultivated Plants or ICNCP.