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Botanical name

A botanical name is the formal scientific designation given to a species of plant, alga, or fungus, adhering to the binomial nomenclature system that combines a capitalized genus name with a lowercase specific epithet, both typically in Latin or Latinized form.^[1] This system, pioneered by Swedish botanist Carl Linnaeus in his seminal 1753 publication Species Plantarum, provides a universal standard for identifying organisms and is regulated by the International Code of Nomenclature for algae, fungi, and plants (ICN), the authoritative set of rules adopted by international botanical congresses.^[2]^[3] The structure of a botanical name ensures precision and consistency; for instance, the sugar maple is denoted as Acer saccharum, where Acer refers to the genus of maples and saccharum describes the species' sugar-producing qualities.^[1] Names are conventionally italicized in print or underlined when handwritten, and they may include an authority abbreviation to credit the original describer, such as Acer saccharum Marsh., honoring botanist Humphry Marshall.^[4] This nomenclature extends beyond species to infraspecific ranks like subspecies or varieties, as well as hybrids indicated by the multiplication sign ×, facilitating detailed taxonomic classification.^[5] Botanical names play a crucial role in scientific research, horticulture, and conservation by eliminating confusion arising from vernacular common names, which can vary widely across cultures and regions—for example, the plant known as "black tupelo," "sour gum," or "pepperidge" in English is universally Nyssa sylvatica.^[1] The classificatory system they form reflects phylogenetic relationships, aiding in the study of biodiversity and evolution, and underpins global databases like the World Flora Online, promoting accurate documentation and protection of plant species.^[6] The ICN, with its latest edition as the Madrid Code (18th edition, published in 2025 following ratification at the 2024 International Botanical Congress), continues to evolve through periodic updates at International Botanical Congresses, ensuring the system's relevance in modern systematics including molecular data.^[2]

Overview and Principles

Definition and Purpose

A botanical name is a formal, Latinized scientific name assigned to taxa of plants, algae, and fungi, governed by the rules and recommendations outlined in the International Code of Nomenclature for algae, fungi, and plants (ICN), with the latest edition being the Madrid Code of 2025.^[2] These names serve as standardized identifiers that ensure clarity and consistency in taxonomic classification, enabling precise reference across global scientific communities, herbaria collections, and conservation efforts.^[7] The primary purpose of botanical names is to provide unique, stable, and universal designations for taxa, minimizing ambiguity that could arise from vernacular or regional synonyms.^[5] This stability is achieved through key principles such as the binomial nomenclature system for species names—typically comprising a genus name followed by a specific epithet—and a hierarchical ranking of taxa from kingdom to infraspecific levels, which reflects evolutionary relationships and phylogenetic structure.^[8] By prioritizing stability over time, the ICN allows names to endure changes in classification while facilitating effective communication in research, agriculture, and biodiversity documentation.^[9] Unlike common names, which vary widely by language, culture, and geography—for instance, the plant known as "daisy" in English might be called "Marguerite" in French or "Gänseblümchen" in German—botanical names are internationally recognized and invariant, promoting unambiguous identification regardless of locale.^[10] The scope of the ICN encompasses names of organisms treated as algae (including both green and non-green algae), fungi, and plants (embryophytes), but excludes animals, which are regulated separately by the International Code of Zoological Nomenclature (ICZN).^[5]

Historical Development

Before the establishment of systematic nomenclature, plant names in the 16th and 17th centuries were typically lengthy polynomials—descriptive phrases in Latin that could span multiple words to capture a plant's characteristics, habitat, or resemblance to other species. These appeared in influential herbals, such as those by Swiss botanist Gaspard Bauhin in his Pinax theatri botanici (1623), where he occasionally employed shorter two-word phrases resembling binomials for genera and species, though full polynomials remained the norm for precise identification.^[11]^[12] The modern binomial system was formalized by Swedish naturalist Carl Linnaeus in his seminal work Species Plantarum (1753), which assigned each plant a two-part name consisting of a genus and a specific epithet, providing a concise and hierarchical framework for classification that revolutionized botany.^[13] This approach built on earlier informal uses but standardized the format, establishing 1753 as the nominal starting point for botanical names under subsequent codes.^[14] The evolution toward codified rules began with the first international agreement at the 1867 Paris Congress, adopting Alphonse de Candolle's Lois de la Nomenclature Botanique to promote uniformity, priority, and stability in naming. Subsequent editions refined these principles: the 1906 Vienna Rules introduced name conservation for genera; the 1935 Cambridge Rules formalized typification and valid publication; and later versions, such as the 1952 Stockholm Code, expanded conservation to higher ranks and introduced autonyms. The code, originally the International Code of Botanical Nomenclature (ICBN), was renamed the International Code of Nomenclature for algae, fungi, and plants (ICN) at the 2011 Melbourne Congress, explicitly incorporating fungi (previously aligned but not fully integrated) and permitting electronic publication from the 2012 edition onward.^[14]^[15] Key shifts emphasized stability through priority (the earliest valid name prevails) while allowing exceptions for conserved names to avoid disruptive changes, alongside progressive inclusion of fungi via sanctioning provisions in 1981 and simplified rules in 2011. The most recent updates appear in the Madrid Code (2025), published on July 21, 2025, adopted at the 20th International Botanical Congress in Madrid, Spain (July 2024), which introduced voluntary registration for plant and algal names and prohibitions on offensive epithets, along with improvements in typification and the handling of digital nomenclatural data.^[8]^[9]^[16] These congresses, held approximately every six years, ratify changes through debated proposals, ensuring the code adapts to scientific advances while maintaining nomenclatural stability.

Forming Botanical Names

Components of Names

Botanical names at the species level consist of two primary components: the genus name and the specific epithet. The genus name forms the first part of the binomial and is a noun in the nominative singular, treated as such even if derived from other languages, written with an initial capital letter and italicized. For example, Rosa denotes the genus encompassing roses and similar plants. According to the International Code of Nomenclature for algae, fungi, and plants (ICN), genus names must be in the Latin alphabet and may be newly formed words, Latinized terms, or hyphenated constructs, but they cannot repeat technical Latin terms used in plant morphology after 1 January 1912 unless accompanied by a species name under the Linnaean system.^[17] The specific epithet comprises the second part, forming a binary combination with the genus name, and is typically an adjective, noun in apposition, or genitive noun, written in lowercase and italicized. It must agree in gender with the genus name when adjectival; for instance, in Rosa canina, "canina" is feminine to match the feminine genus Rosa. Epithets can derive from any source, including personal names (e.g., linnaeana honoring Linnaeus) or geographic terms (e.g., alpina for alpine regions), but tautonyms—where the epithet repeats the genus name, such as Rosa rosa—are invalid. Gender corrections, if needed, are orthographic adjustments that do not affect the name's validity or priority.^[18]^[19] Orthographic rules ensure consistency in spelling and form under ICN Article 60, which mandates retention of the original spelling except for typographical or orthographical errors causing confusion. Diacritical signs, such as umlauts or accents, are generally replaced by plain letters or digraphs (e.g., ä becomes ae in Mägdéburg to Maedéburg), though ligatures like æ in Æsculus (now standardized as Aesculus) may be used but are not required. Transliteration from non-Latin scripts follows Latin alphabet equivalents, standardizing ancient forms (e.g., u/v and i/j interchanged as in classical Latin) and permitting letters like k, w, and y for modern adaptations, such as from Greek (k for kappa) or indigenous languages. Misspellings are correctable without altering the name's legitimacy, preserving the intent of the original publication.^[19]^[17] In scientific literature, abbreviations facilitate reference to taxa without full names, particularly when specificity is unnecessary. The abbreviation "sp." denotes an unspecified species within a genus (e.g., Rosa sp.), while "spp." indicates multiple unspecified species (e.g., Rosa spp.); these are not formal names but conventional shorthand. Full forms are preferred in formal contexts, with abbreviations used sparingly to avoid ambiguity, as per ICN recommendations. Although higher infraspecific ranks like subspecies use "ssp." or "subsp.," the core species-level components emphasize complete binomials for precision.^[17] While species-level names form the foundation of botanical nomenclature, higher ranks build upon them with standardized endings: families end in "-aceae" (e.g., Rosaceae from Rosa), derived from the type genus, and orders in "-ales" (e.g., Rosales). These suffixes ensure uniformity, with exceptions for well-established pre-ICN names, but the binomial structure at genus and species remains the essential unit for identification and classification.

Binomial Nomenclature

Binomial nomenclature is the system used in botany to name species with a two-part Latin or Latinized name consisting of a genus name followed by a specific epithet. The genus name, a singular noun capitalized and typically italicized, identifies the broader group, while the specific epithet, uncapitalized and also italicized, denotes the particular species within that genus. For example, the English oak is named Quercus robur, where Quercus is the genus and robur (meaning "strong" or "hard") is the epithet describing the tree's robust wood.^[20] This format ensures unambiguous identification and promotes stability in scientific communication, as mandated by Article 23 of the International Code of Nomenclature for algae, fungi, and plants (ICN).^[20] The formation of binomial names follows strict rules to maintain consistency and avoid redundancy. The specific epithet must not repeat the genus name, prohibiting tautonyms such as Quercus quercus.^[20] Adjectival epithets must agree in gender, number, and case with the genus name; for instance, the genus Rubus (masculine) pairs with idaeus in Rubus idaeus (raspberry), but would adjust to idaeus if the genus were feminine.^[20] Nouns in the genitive case, such as those honoring persons (e.g., banksii for Joseph Banks), do not change form. Each genus requires a designated type species to fix its application, such as Rosa cinnamomea L. serving as the type for the genus Rosa, ensuring the name's circumscription remains tied to a reference point despite taxonomic revisions.^[20]^[21] Exceptions to the standard binomial exist for specific cases. Genera are named with monomials—single nominative singular nouns—without an epithet, as in Poa for bluegrasses.^[20] Hybrids at the species or genus level use nothotaxa, indicated by a multiplication sign "×" placed before the name (e.g., Salix × capreola for a willow hybrid) or between parent genera for intergeneric hybrids (e.g., ×Cupressocyparis for cypress hybrids), often accompanied by a formula listing parentage like Cupressus × Chamaecyparis.^[20] To enhance nomenclatural stability, particularly for economically or culturally important taxa, the ICN allows conservation of names under Appendix B, protecting widely used but technically illegitimate binomials against earlier synonyms or homonyms; for example, Malvaceae is conserved to maintain familial stability.^[20] This mechanism corrects common misnomers, such as replacing invalid tautonyms or homonyms with conserved alternatives, without disrupting established usage.^[20]

Infraspecific and Infragenic Names

In botanical nomenclature, infraspecific names designate taxa ranked below the species level, extending the binomial species name into a trinomial or higher combination to reflect variation within a species. These names are governed by the International Code of Nomenclature for algae, fungi, and plants (ICN), which recognizes principal ranks such as subspecies (abbreviated subsp. or ssp.), variety (var.), and form (f.), while permitting additional subordinate ranks like subvariety, subform, and others. The formation follows a trinomial structure: the genus name, specific epithet, rank-denoting abbreviation in Roman type, and an italicized infraspecific epithet in lowercase, with no repetition of higher-level epithets unless forming an autonym.^[22] For example, the pedunculate oak is named Quercus robur subsp. pedunculata, where "pedunculata" denotes a subspecies distinguished by morphological traits like acorn stalk length.^[22] The choice of infraspecific rank often reflects the nature of variation: subspecies (subsp.) typically denotes geographically isolated or ecologically distinct populations, while varieties (var.) highlight morphological differences, and forms (f.) capture minor, often non-heritable traits such as leaf color.^[23] All components of the name except the rank abbreviation are italicized, and the infraspecific epithet must agree grammatically in gender, number, and case with the specific epithet it modifies.^[18] Priority operates within each rank, meaning the earliest validly published legitimate name at that rank takes precedence, but names at different infraspecific ranks do not compete.^[24] Autonyms are automatically established when a new infraspecific name is published; for instance, naming Rosa canina subsp. lutetiana creates the autonym Rosa canina subsp. canina for the residual portion including the species type.^[25] Intraspecific hybrids are indicated by inserting the multiplication sign × before the infraspecific epithet, as in Mentha spicata var. × piperita, though such names must still comply with trinomial formation rules.^[22] Infragenic names apply to taxa ranked between the genus and species levels, organizing species within a genus into subgroups based on shared characteristics. Common ranks include subgenus (subg.), section (sect.), and series (ser.), with the ICN allowing further subdivisions like subsection (subsect.) and subseries (subser.) without a fixed limit, provided the rank is explicitly indicated for names published after 1952.^[26] These names are formed by placing the rank-denoting term (in Roman type) after the genus name, followed by a plural adjectival epithet in italics that agrees in gender with the genus; for example, Rosa sect. Caninae groups dog roses within the genus Rosa.^[24] Unlike infraspecific names, infragenic epithets are typically plural to reflect collective taxa, and no connecting term like "of" is used.^[27] Priority for infragenic names applies separately at each rank, with the correct name being the one with the earliest valid publication date at that level within the genus.^[24] Autonyms are also generated automatically for subdivisions; publishing Solanum subg. Leptostemonum establishes Solanum subg. Solanum for the type-inclusive remainder. These ranks facilitate hierarchical classification, such as using sections for major morphological clades and series for finer groupings, enhancing the organization of diverse genera like Quercus or Carex.^[26] All such names must be validly published with a description or diagnosis and a designated type, ensuring stability in taxonomic revisions.^[28]

Typification and Circumscription

Type Specimens

In botanical nomenclature, a type specimen serves as the permanent nomenclatural reference point that fixes the application of a scientific name to a particular taxon, ensuring stability and objectivity in taxonomy. Under the International Code of Nomenclature for algae, fungi, and plants (ICN), type specimens are essential for typification, as outlined in Articles 9 and 10, where they anchor the name to a specific morphological or genetic identity.^[7] The primary categories of type specimens include the holotype, which is the single specimen or illustration used by the original author to describe the taxon and explicitly designated as such in the protologue (the original publication). Duplicates of the holotype, known as isotypes, provide additional material from the same collection event and are treated equivalently for identification purposes. If no holotype was designated or if the original material consists of multiple specimens (syntypes), a lectotype is selected later from that material to serve as the type; similarly, a neotype is chosen when all original material is lost or destroyed, provided no prior type exists. An epitype may be designated to supplement and clarify an existing holotype, lectotype, or neotype when the original type is ambiguous, incomplete, or lacks sufficient detail for precise identification, such as in cases involving molecular data or subtle morphological traits.^[7]^[29] Designation of types must be explicit, either in the protologue or through a subsequent legitimate publication, with the location (e.g., herbarium acronym) clearly indicated to facilitate verification. For names published by Carl Linnaeus in Species Plantarum (1753), which form the starting point for modern botanical nomenclature, types were not originally designated, so lectotypes or neotypes have been assigned retrospectively through ongoing international efforts to stabilize nomenclature. These retrospective typifications often draw from Linnaean herbarium collections now housed in institutions like the Linnean Society of London.^[7]^[30] Type specimens are required to be preserved in recognized herbaria or other permanent collections to ensure long-term accessibility for taxonomic study, with the Index Herbariorum serving as the authoritative global directory of such institutions holding over 350 million specimens. Since the Shenzhen Code (2018), digital images of physical specimens have been accepted as equivalent to the specimens themselves for typification purposes, provided they are permanently accessible and of sufficient quality; the Madrid Code (2025) further updated these provisions to explicitly include electronic types derived from digital imaging protocols. Epitypes must also be deposited similarly and explicitly linked to the original type with detailed justification.^[31]^[7] The 2025 Madrid Code introduced expanded rules for voluntary registration of type specimens in centralized databases, such as those integrated with Index Herbariorum, to enhance traceability and global access, particularly for digital and epitype designations. This facilitates typification while maintaining the conceptual boundaries of taxa by providing a verifiable anchor for circumscription.^[7]^[8]

Taxon Circumscription

Taxon circumscription delineates the boundaries of a taxonomic group through its morphological, genetic, or ecological characteristics, with the nomenclatural type serving as the permanent reference point for applying the name, as outlined in the Preamble to the International Code of Nomenclature for algae, fungi, and plants (ICN).^[32] While the name itself lacks a circumscription, the taxon it denotes is defined by these limits, which are determined by taxonomic judgment rather than nomenclatural rules; the type ensures stability by linking the name to a specific specimen or illustration, regardless of evolving taxonomic interpretations.^[32] This approach allows the scope of the taxon to expand or contract based on evidence, but the name remains attached to the type, preventing arbitrary reassignment. Over time, circumscription undergoes revision through taxonomic research, involving the splitting or merging of taxa via new combinations or the designation of synonyms, provided such changes are supported by substantive evidence beyond the name alone, such as comparative morphology or molecular data.^[8] For instance, post-2000 advancements in DNA barcoding have prompted significant shifts; in the genus Primula (Primulaceae), barcoding analyses using markers like rbcL and matK revealed cryptic diversity, leading to refined circumscriptions that separated entities previously lumped under broader species concepts, such as distinguishing P. wilsonii from related taxa based on genetic divergence.^[33] These revisions highlight how phylogenetic evidence can redefine limits, contrasting traditional Linnaean hierarchies with clade-based approaches that emphasize monophyly over rank-based categories.^[34] In taxonomy, circumscription plays a crucial role in ensuring that a name accurately applies to the intended organisms, facilitating communication and stability across studies; the type specimen acts as the fixed anchor for this process, allowing reinterpretation without altering the name's validity.^[32] When multiple names refer to the same circumscribed taxon, the senior synonym—the earliest validly published name—prevails under the ICN's Principle of Priority (Art. 11), rendering later names synonymous unless conserved otherwise. Comprehensive lists of synonyms and current circumscriptions are maintained in authoritative databases, such as Tropicos, which aggregates over 1.3 million plant names with synonymy details, and Plants of the World Online (POWO), which integrates phylogenetic data to reflect ongoing taxonomic delimitations.

Authority, Validity, and Priority

Author Citation

In botanical nomenclature, author citations attribute scientific names to the individuals responsible for their valid publication, typically appended to the binomial or other taxonomic name in abbreviated form. This practice honors the taxonomists involved and provides traceability to the original description, as governed by Article 46 of the International Code of Nomenclature for algae, fungi, and plants (ICN).^[35] For instance, the name Rosa canina L. credits Carl Linnaeus, abbreviated as "L.", for its establishment.^[36] Standard abbreviations for authors' names are prescribed in Appendix II of the ICN, which draws from the authoritative reference Authors of Plant Names by Brummitt and Powell (1992), with ongoing updates to ensure consistency and distinctiveness—abbreviations should be long enough to avoid ambiguity and usually end with a consonant.^[5] The International Plant Names Index (IPNI) serves as the primary database for these standardized forms, compiling approximately 1.4 million records of vascular plant names with verified author abbreviations to facilitate global use.^[36] For multiple authors, the connective "et" (Latin for "and") is employed, as in "Hook. f. et Thoms." for Joseph Dalton Hooker the younger and another collaborator, while "et al." may abbreviate longer lists in recommendations but not in formal citations.^[35] The distinction between basionym authors and combining authors is crucial for names resulting from transfers or new combinations. A basionym is the original legitimate name upon which a new name is based, and its author is cited first; the combining author, who effects the transfer to a different taxon, follows, often connected by a comma or semicolon. For example, in Festuca ovina L. subsp. capitata (Vill.) Arcangeli, the basionym Festuca capitata Vill. is transferred to a subspecies under F. ovina, so the full citation credits both Vill. for the basionym and Arcangeli for the combination.^[35] When the basionym author did not validly publish but their work was later validated by another, "ex" precedes the basionym author, as in Sicyos triqueter Moc. & Sessé ex Ser., where Mocino and Sessé proposed it and Ser. validly published.^[35] Author citations may be omitted in specific cases to maintain clarity and avoid misleading attributions. For anonymous publications, no author is cited, as the responsibility lies with the publication itself rather than an identifiable individual.^[35] Similarly, for later homonyms—names identical to earlier ones but illegitimate due to priority—citations are typically excluded to prevent confusion with the valid earlier name.^[35] The Madrid Code (2025 edition), effective following the Twentieth International Botanical Congress in 2024, supersedes the Shenzhen Code (2018) without substantive changes to core author citation rules but reinforces standardization amid increasing electronic publications, including provisions for digital accessibility of nomenclatural acts.^[8]

Publication and Legitimacy

For a botanical name to be validly published under the International Code of Nomenclature for algae, fungi, and plants (ICN, Madrid Code 2025), it must first be effectively published, meaning issued in a scientific journal or book bearing an International Standard Serial Number (ISSN) or International Standard Book Number (ISBN), a requirement established on 1 January 2012.^[7] Prior to 2012, effective publication could occur in other printed media, but post-2012 standards ensure permanence and accessibility. Additionally, since 1 January 2012, electronic publications qualify as effectively published only if they are assigned a persistent identifier, such as a Digital Object Identifier (DOI), as mandated by the Madrid Code to facilitate long-term retrieval.^[5] The validating description or diagnosis of a new taxon must include Latin for publications before 1 January 2012, but since then, it may be provided in English or any other language, broadening accessibility while maintaining scientific rigor.^[9] A validly published name is legitimate if it complies with the ICN's provisions on form, type designation, and absence of conflicts, ensuring it does not perpetuate errors or redundancies in nomenclature. Specifically, legitimacy requires that the name is not a later homonym—identical to an earlier legitimate name for a different taxon at the same rank—as later homonyms are illegitimate under Article 53. It must also adhere to nomenclatural type requirements, where the type (e.g., a specimen or illustration) effectively fixes the application of the name, though detailed typification rules apply separately. Furthermore, the Madrid Code prohibits certain forms, including offensive or derogatory epithets; for instance, new Article 51.2, effective 1 January 2026, allows the rejection of such names for newly proposed taxa or replacement names, while specific offensive terms like "caffra" are retroactively amended to "afra" in over 300 existing names to eliminate derogatory connotations.^[7]^[9] Names failing these criteria are invalid or illegitimate. Invalid names include nomina nuda, which are published without a required Latin (pre-2012) or any-language (post-2012) description or diagnosis under Articles 32 and 38, rendering them unavailable for use. Other invalid or suppressed names arise under Articles 32–45, which govern valid publication requirements, or specific illegitimacy provisions such as Article 52 (superfluous names) and Article 56 (suppression for stability). For example, names that are later homonyms or violate form rules (e.g., Article 23 on orthography) may be suppressed to prevent confusion.^[5]^[7] Since the Madrid Code's adoption in 2025, registration of new names has become a key step for legitimacy, particularly for fungi, where it has been mandatory since 2013 in designated repositories like MycoBank to ensure traceability and prevent duplication. For algae, fungi, and plants, the Code now establishes a framework overseen by a new Registration Committee, with mandatory proactive registration for fungal names and voluntary but recommended registration for algal and plant names in repositories such as the International Plant Names Index (IPNI), effective from the 2024 International Botanical Congress decisions incorporated in 2025. This system enhances nomenclatural stability by linking new names to persistent digital records.^[9]^[8]

Principle of Priority

The Principle of Priority establishes that, among multiple legitimate names proposed for the same taxon at the same rank, the earliest validly published name—known as the senior synonym—takes precedence and is the correct name to use. This rule, codified in Article 11 of the International Code of Nomenclature for algae, fungi, and plants (ICN), applies only after names have been determined to be validly published and legitimate, resolving conflicts to ensure nomenclatural stability without regard to taxonomic judgments.^[24] For most plant taxa, priority dates from 1 May 1753, the publication date of Carl Linnaeus's Species Plantarum (edition 1), serving as the starting point for names at the rank of genus and below in spermatophytes and pteridophytes. Names published before this date are generally not considered for priority, though certain pre-1753 names may be retroactively applied in specific historical contexts under ICN provisions. For pteridophytes, while the primary starting point aligns with 1753, earlier codes like the Paris Code of 1900 influenced transitional rules for some fern nomenclature, now unified under the modern ICN framework. Fungi and algae follow similar principles but may have group-specific starting points, such as later dates for certain fungal lineages.^[37]^[8] Exceptions to absolute priority allow for the conservation of names to avoid nomenclatural instability, as detailed in ICN Article 14 and Appendix B. Conserved names (nomina conservanda) are explicitly protected against competing senior synonyms or homonyms if their displacement would cause significant disadvantage, with over 1,000 such names listed across appendices for families (Appendix IIA/IIB), genera (Appendix III), and species (Appendix IV). For instance, the genus name Rosa is conserved against earlier synonyms to preserve long-established usage in rosaceous taxonomy. These decisions are made by international committees, such as the Committee for Vascular Plants, ensuring priority is limited only when necessary for practical stability.^[8]^[38] Homonymy, treated under ICN Article 53, renders later identical names illegitimate regardless of priority, as they duplicate earlier validly published names for different taxa and must be rejected unless explicitly conserved. The 2025 Madrid Code introduces strengthened recommendations for using searchable online databases, like the International Plant Names Index (IPNI) and World Flora Online, to check for existing homonyms prior to new publications, reducing inadvertent illegitimacy and enhancing global compliance.^[39]^[8] In taxonomic practice, the Principle of Priority guides the construction of synonymy lists, where nomenclatural synonyms—competing names based on the same type and resolved by date of publication—are clearly differentiated from taxonomic synonyms, which involve distinct types but synonymous application based on biological evidence. This distinction maintains the objectivity of nomenclature separate from evolving taxonomic interpretations. Valid publication remains the foundational prerequisite, as only names meeting ICN criteria for effective and valid publication can invoke priority.^[24]

Special Cases and Exceptions

Names in Cultivated Plants

The International Code of Nomenclature for Cultivated Plants (ICNCP), in its ninth edition published in 2016, provides the governing rules for naming cultivated plants, known as cultigens, which are distinct from the nomenclature of wild plants regulated by the International Code of Nomenclature for algae, fungi, and plants (ICN).^[40] The ICNCP applies specifically to cultivars—assemblages of cultivated plants that are distinct, uniform, and stable in their characteristics due to human selection and propagation—and to cultivar groups, which are formal categories aggregating related cultivars or plants sharing similar traits within a genus or lower taxon.^[40] Unlike the ICN, which uses Latinized binomial names for wild taxa, the ICNCP operates as a separate system, where cultivar epithets are not considered validly published under ICN rules and do not interfere with wild plant nomenclature.^[40] Cultivar names are formed by appending a cultivar epithet in single quotation marks to the name of the underlying taxon, typically a genus or species name from the ICN, without Latinization for epithets established after January 1, 1959; these epithets must use modern language and are limited to 30 characters since January 1, 1996.^[40] For example, the hybrid tea rose is denoted as Rosa ‘Peace’, where ‘Peace’ is the non-Latinized epithet.^[40] Cultivar groups are named by adding the term "Group" (or its abbreviation "Gp.") to a descriptive epithet, such as Brassica oleracea Gemmifera Group for Brussels sprouts cultivars, without quotation marks.^[40] Trade designations, which are unregulated marketing names, may accompany formal cultivar names, as in Dianthus FANTASIA ‘Londaison’, where FANTASIA serves commercial purposes but holds no nomenclatural status.^[40] In orchids, the term "grex" (or "gx.") designates the progeny from a specific cross between two parent plants, acknowledging clonal variation while grouping similar offspring; for instance, Paphiopedilum Sorel grex refers to clones from that cross, and additional cultivar epithets like ‘Alba’ can be appended for specific selections.^[40] Hybrid cultivated plants incorporate the multiplication sign "×" before the name, following ICN conventions for hybrid formulas, such as Rosa × borboniana ‘Boule de Neige’ for a hybrid cultivar.^[40] Epithets for cultivated hybrids do not establish priority under the ICN but are governed solely by ICNCP provisions.^[40] Priority for cultivar and group names under the ICNCP is determined by the date of registration rather than publication, ensuring stability through official documentation; names must be registered with an International Cultivar Registration Authority (ICRA) to be validly established.^[40] ICRAs, appointed by the International Society for Horticultural Science, handle specific plant groups—for example, the Royal Horticultural Society serves as ICRA for roses, maintaining records since 1955, while the American Rose Society also registers modern roses.^[40]^[41] This registration process promotes international uniformity and prevents duplication, with statutory protections in some jurisdictions superseding ICNCP priority where applicable.^[40]

Hybrid and Graft Names

In botanical nomenclature, hybrids between taxa are denoted using the multiplication sign × to indicate their parentage, as governed by Appendix I of the International Code of Nomenclature for algae, fungi, and plants (ICN). For an intergeneric hybrid, the × precedes the name of the hybrid genus or the specific epithet, such as in Mentha × piperita L., which results from M. aquatica L. × M. spicata L.. For intraspecific or interspecific hybrids within the same genus, the × is placed between the names of the parent taxa in a hybrid formula, for example, Lychnis chalcedonica (Ehrh. ex L.f.) × L. coronaria (Desr.) to denote the parentage of L. × haageana Regel. These notations apply to both naturally occurring and cultivated hybrids, ensuring clarity in indicating hybrid origin without altering the binomial structure for the hybrid taxon itself.^[8] The legitimacy and priority of hybrid names follow specific rules in ICN Appendix I. A hybrid name is legitimate only if both parent taxa have validly published names, and for a nothotaxon at the rank of species or below, the publication must include a description or diagnosis along with the hybrid formula specifying parentage (Art. H.9.1). Priority for hybrid names is established from the date of valid publication, independent of the parents' names, allowing the earliest validly published hybrid name to take precedence even if later parentage is clarified (Art. H.10). These provisions ensure that hybrid nomenclature remains stable and traceable, applicable across wild and cultivated contexts unless supplemented by the International Code of Nomenclature for Cultivated Plants (ICNCP) for cultigens.^[8] Graft chimeras, which arise from the fusion of tissues from different taxa rather than sexual hybridization, are distinguished by the addition sign + placed between the names of the component taxa. For instance, Laburnum × watereri (Dipp.) × Cytisus purpureus Scop. forms the graft chimera denoted as Laburnum × watereri + 'Vossii', where the + indicates the chimeric nature involving multiple tissue layers from the parents. This notation is reserved for true graft hybrids and does not confer species rank, emphasizing the structural rather than genetic hybridity (ICN Art. H.4). Such names are validly published under similar legitimacy rules as sexual hybrids but are rare and typically encountered in horticultural documentation.^[8]^[40] In cultivated plants, hybrid notation integrates with cultivar naming under the ICNCP, which supplements the ICN for horticultural taxa. The × may appear in the hybrid formula preceding the cultivar name, as in Iris pseudacorus L. × I. versicolor L. 'Absolute Treasure', where the cultivar epithet follows the indicated hybrid parentage in single quotes. Cultivated hybrid names are registered separately through international authorities to track parentage and avoid duplication, maintaining consistency with wild hybrid rules while accommodating selection and propagation in cultivation. Intraspecific hybrids may reference subordinate ranks briefly, such as varietal parents, but follow the same × notation without mandatory infraspecific indicators.^[40]

Fossil and Extinct Taxa Names

The International Code of Nomenclature for algae, fungi, and plants (ICN) applies to fossil taxa, with Article 13 specifying that names for fossil organisms (except diatoms) have a nomenclatural starting point of 31 December 1820, based on works such as Sternberg's Flora der Vorwelt and Schlotheim's Petrefactenkunde.^[37] Names of fossil taxa are established based on preserved plant parts or organs, such as leaves, stems, or reproductive structures, rather than requiring evidence of the whole organism; for example, the genus Archaeopteris was named for Devonian fossil fronds that later contributed to reconstructing progymnosperm plants.^[37] In paleobotany, morphotaxa—also known as form-genera or organ-genera—are commonly used for isolated fossil parts that cannot be confidently linked to a single biological species, allowing flexible naming without implying phylogenetic relationships; the genus Sigillaria, for instance, denotes impressions of Carboniferous lycopod stems, encompassing various preservation states like adpressions or petrifactions, but typically without infraspecific ranks due to the artificial nature of such groupings. Types for fossil taxa can be physical specimens, such as compressed fossils or permineralized material, and priority follows ICN rules from the 1820 starting point, though conflicts are rare and often resolved through conservation proposals under Article 14.^[37] Extinct taxa from recent historical periods, such as the plant Silphium (an Apiaceae likely harvested to extinction around the 1st century CE in ancient Cyrenaica), are treated under the ICN as wild species despite lacking living representatives, with nomenclature following standard rules for non-fossil taxa unless fossilized remains are designated as types. The 2025 Madrid Code includes clarifications on the nomenclature of fossil-taxa and the removal of impediments to their typification.^[10]

References

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### Summary of Article 24: Names of Infraspecific Taxa
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