The latest, updated edition of the essential, authoritative reference for botanical, mycological, and phycological names.   The International Code of Nomenclature for algae, fungi, and plants, known as “the Code,” is the set of internationally agreed rules and recommendations that govern the naming of these organisms. Scientific naming has deep historical roots. Indeed, the system of naming organisms is one of the first truly global scientific standards. This essential reference originates in Alphonse de Candolle’s 1867 Lois de la nomenclature botanique. This 2025 edition of the Code, the Madrid Code, reflects the decisions made at the Twentieth International Botanical Congress, which met in Madrid, Spain, in July 2024. The congress debated 447 proposals to amend the Code and accepted important new rules, including a mechanism for voluntary registration of plant and algal names, clarifications for naming fossil taxa, the option to reject a new name if it is derogatory to a group of people, and the replacement of an epithet that was considered particularly offensive (revising to afra, afrorum, and afrum).

Table of Contents:
Preface Key to renumbering between the Shenzhen Code and the Madrid Code Important dates in the Code Latin terms and their abbreviations used in the Code Preamble   Division I. Principles      Principle I. Independence      Principle II. Types      Principle III. Priority      Principle IV. Single correct name      Principle V. Latin names      Principle VI. Retroactivity   Division II. Rules and Recommendations      Chapter I. Taxa and their ranks                Article 1. Taxa                Article 2. Ranks                Article 3. Principal ranks                Article 4. Secondary and further ranks                Article 5. Order of ranks      Chapter II. Status, typification, and priority of names           Section 1. Status definitions                Article 6           Section 2. Typification                Article 7. Typification in general                Article 8. Specimens and gatherings                Article 9. Categories and designation of types                Article 10. Typification of names above the rank of species           Section 3. Priority and status of names                Article 11. Priority of names                Article 12. Status of names           Section 4. Limitation of priority                Article 13. Nomenclatural starting-points                Article 14. Conserved names                 [Article 15. Sanctioned names – see Article F.3]      Chapter III. Nomenclature of taxa according to their rank           Section 1. Names of taxa above the rank of family                Article 16. Names above the rank of family                Article 17. Names of orders and suborders           Section 2. Names of families, subfamilies, tribes, and subtribes                Article 18. Names of families                Article 19. Names of subfamilies, tribes, and subtribes           Section 3. Names of genera and subdivisions of genera                Article 20. Names of genera                Article 21. Names of subdivisions of genera                Article 22. Autonyms of subdivisions of genera           Section 4. Names of species                Article 23           Section 5. Names of taxa below the rank of species (infraspecific taxa)                Article 24. Names of infraspecific taxa                Article 25. Sum of subordinate taxa                Article 26. Autonyms of infraspecific taxa                Article 27. Final epithet in names of infraspecific taxa           Section 6. Names of organisms in cultivation                Article 28      Chapter IV. Effective publication                Article 29. Definition and conditions of effective publication                Article 30. Further conditions of effective publication                Article 31. Date of effective publication      Chapter V. Valid publication           Section 1. Valid publication in general                Article 32. General requirements for valid publication                Article 33. Date of valid publication                Article 34. Suppressed works                Article 35. Further requirements for valid publication                Article 36. Names not accepted by their authors, alternative names                Article 37. Requirement of indication of rank           Section 2. Valid publication of names of new taxa                Article 38. Requirement of description, diagnosis, or illustration with analysis                Article 39. Language of validating description or diagnosis                Article 40. Requirement of indication of type           Section 3. New combinations, names at new rank, and replacement names                Article 41           Section 4. Registration of names and nomenclatural acts                Article 42           Section 5. Names in particular groups                Article 43. Names of fossil-taxa                Article 44. Names of algae                Article 45. Names in groups covered by other Codes      Chapter VI. Citation of names                Article 46. Author citations                Article 47. Names of altered taxa without exclusion of type                Article 48. Names of altered taxa with exclusion of type                Article 49. Parenthetical author citations                Article 50. Transfer between the hybrid and non-hybrid category                General recommendations on citation [Recommendations 50A–50G]      Chapter VII. Rejection of names                Article 51. Limitation of rejection                Article 52. Nomenclaturally superfluous names                Article 53. Homonyms                Article 54. Inter-Code homonymy                Article 55. Limitation of illegitimacy                Article 56. Rejected names                Article 57. Names used for taxa not including their types                Article 58. Reuse of illegitimate names                 [Article 59. Names of fungi with a pleomorphic life cycle – see Article F.8]      Chapter VIII. Orthography and gender of names                Article 60. Orthography of names                Article 61. Orthographical variants of names                Article 62. Gender of names      Chapter F. Names of organisms treated as fungi (Maastricht version)           Section 1. Limitation of priority                Article F.1. Nomenclatural starting-point                Article F.2. Protected names                Article F.3. Sanctioned names           Section 2. Valid publication and typification of names                Article F.4. Misplaced rank-denoting terms                Article F.5. Registration of names and nomenclatural acts           Section 3. Rejection of names                Article F.6. Homonyms                Article F.7. Rejected names           Section 4. Names of fungi with a pleomorphic life cycle                Article F.8           Section 5. Orthography of names                Article F.9           Section 6. Author citations                Article F.10           Section 7. Recommendations on types that are living cultures                Recommendation F.11A      Chapter H. Names of hybrids                Article H.1. Indication of hybrids                Article H.2. Hybrid formulae                Article H.3. Names of nothotaxa                Article H.4. Circumscription of nothotaxa                Article H.5. Ranks of nothotaxa                Article H.6. Nothogeneric names and condensed formulae                Article H.7. Hybrids between subdivisions of genera                Article H.8. Parentage, nothogeneric names, and condensed formulae                Article H.9. Valid publication of names of nothogenera and their subdivisions                Article H.10. Valid publication of names of nothospecies and infraspecific nothotaxa                Article H.11. Nothotaxa with parents belonging to different higher-ranked taxa                Article H.12. Subordinate taxa within nothospecies   Division III. Provisions for governance of the Code      Provision 1. General provisions for governance of the Code      Provision 2. Proposals to amend the Code      Provision 3. Institutional votes      Provision 4. Nomenclature Section      Provision 5. Procedures and voting at the Nomenclature Section      Provision 6. After an International Botanical Congress      Provision 7. Permanent Nomenclature Committees [Membership, Functions, Procedural rules]      Provision 8. Provisions for governance of the Code relating solely to names of organisms treated as fungi   Glossary. Definitions of terms used in this Code Appendices I–VII Index of scientific names Subject index