PhyloCode: Glossary

acceptable name: An established name that is not a (non-conserved) later homonym and thus may potentially be an accepted name.
accepted name: The name that must be adopted for a clade under this code.
ancestor: An entity from which another entity is descended.
apomorphy (apomorphic): A derived character state; a new feature that arose during the course of evolution (see synapomorphy).
apomorphy-modified crown-clade definition: A minimum-clade definition that is modified by the use of an apomorphy to define the name of a crown clade. See Article 9.9.
apomorphy-based definition: A definition that associates a name with a clade originating in the first ancestor to evolve a specified apomorphy that was inherited by one or more internal specifiers. See Article 9.7.
apomorphy-modified node-based definition: A term used in earlier versions of this code that is roughly equivalent to an apomorphy-modified crown-clade definition in this version (see footnote to Art. 9.9).
binomen (binomina): A name composed of two words; commonly used to refer to species names composed of a generic name and a specific name (ICZN) or epithet (ICNP, ICNAFP) under the rank-based codes.
branch: An edge or internode (connection between two nodes) on a tree (in the sense of graph theory). On a phylogenetic tree, a branch is commonly used to represent (1) a lineage between two splitting events (internal branch), or between a splitting event and an extinction event (terminal branch) or between a splitting event and a specified time, often the present (terminal branch), or (2) an ancestor-descendant relationship. The term is sometimes also used (but not in this code) for an internode and all nodes and internodes distal to (descended from) it.
branch-based definition: A term used in earlier versions of this code that is roughly equivalent to a maximum-clade definition in this version (see footnote to Art. 9.5).
branch-modified node-based definition: A term used in earlier versions of this code that is roughly equivalent to a maximum-crown-clade definition in this version (see footnote to Art. 9.5).
categorical rank (also taxonomic rank): A formal category denoting position in a hierarchy of nested taxa. The categorical ranks commonly used in taxonomy comprise seven principal categories (kingdom, phylum or division, class, order, family, genus, and species), which are often treated as mandatory, as well as additional primary categories (e.g., cohort, tribe) and secondary categories (e.g., superorder, subfamily). Note that the species category is treated as a rank in rank-based nomenclature, even when it is conceptualized as a category of biological entities.
clade: An ancestor (an organism, population, or species) and all of its descendants.
conditionally suppressed name: A name that is suppressed only in phylogenetic contexts in which it is a synonym of a particular conserved name (see suppressed name).
conserved name: An established name that the Committee on Phylogenetic Nomenclature has ruled should have precedence over earlier synonyms or homonyms.
conversion: The act of establishing a preexisting name in accordance with the rules of this code.
converted (clade) name: A preexisting name that has been established in accordance with the rules of this code (see new (clade) name).
crown-based total-clade definition: A total-clade definition that is formulated through reference to the corresponding crown clade. See Article 9.10.
crown clade: A clade originating in the most recent common ancestor of two or more extant species (or organisms). See Article 2.2.
crown-clade definition: A phylogenetic definition that necessarily identifies a crown clade (Art. 2.2) as the referent of a taxon name. See Article 9.9.
definition: A statement specifying the meaning of a name; in this code, it is a statement specifying the taxon to which the name refers.
definitional author: The person(s) who published a phylogenetic definition for a name—either the original definition or an emended one (see nominal author).
description: A statement of the features of a taxon (or its component organisms), not limited to those that distinguish it from other taxa with which it might be confused (see diagnosis).
diagnosis (diagnoses): A statement of the features of a taxon (or its component organisms) that collectively distinguish it from other taxa with which it might be confused.
directly-specified-ancestor definition: A kind of minimum-clade definition in which the ancestor in which the clade originated is specified directly rather than indirectly through its descendants. See Note 9.5.1.
emendation: A formal change in the phylogenetic definition of a name.
epithet: In the ICNAFP, a word that, when combined with the name of a genus, forms the name of an infrageneric taxon (e.g., species, subgenus, section, series) or, when combined with the name of a species, forms the name of an infraspecific taxon (e.g., subspecies, variety, form). The ICNP also uses the term “epithet” but only at and below the species rank.
established name: A name that is published in accordance with Article 7 of this code, which may or may not be an acceptable or accepted name.
extant (of a taxon): Having one or more living representatives (organisms) at the present time, or at some specified time since humans began keeping written historical records.
external specifier: A species or specimen that is explicitly excluded from the clade whose name is being defined (see Art. 11.2). Maximum-clade and maximum-crown-clade definitions have external specifiers, but minimum-clade, minimum-crown-clade, apomorphy-based and apomorphy-modified crown-clade definitions normally do not (unless external specifiers are used to prevent use of a name under certain hypotheses of relationships, clade composition, or both; see Art. 11.13).
genus (genera): One of the categorical ranks of rank-based nomenclature; more specifically, it is the primary rank above the rank of species and below that of family. The genus rank is mandatory in rank-based nomenclature not only because it is one of the seven principal ranks (kingdom, phylum or division, class, order, family, genus, species), which are commonly treated as mandatory, but also because the generic name is part of the species binomen.
heterodefinitional: Based on different phylogenetic definitions (see synonym).
homodefinitional: Based on the same phylogenetic definition (see synonym).
homologous: Shared by virtue of inheritance from a common ancestor. A character or character state shared by two organisms (which may represent different species or clades) is said to be homologous if that character or character state was present in all of their ancestors back to and including their most recent common ancestor.
homonym: A name that is spelled identically to another name that refers to a different taxon. See Article 13.1.
hybrid formula: An expression consisting of the names of two taxa separated by a multiplication sign, designating a single organism or set of organisms of hybrid origin.
ICNAFP: International Code of Nomenclature for Algae, Fungi, and Plants.
ICNP: International Code of Nomenclature of Prokaryotes.
ICVCN: International Code of Virus Classification and Nomenclature.
ICZN: International Code of Zoological Nomenclature.
infraspecific epithet: Under the ICNAFP, the third word in an infraspecific trinomen.
infraspecific name: Under the ICZN, the third word in an infraspecific trinomen.
infraspecific taxon: Under the rank-based codes, a taxon below the rank of species.
internal specifier: A species, specimen, or apomorphy that is explicitly included in the clade whose name is being defined (see Art. 11.2). Every phylogenetic definition has at least one internal specifier, and all of the specifiers in minimum-clade, minimum-crown-clade, apomorphy-based, and apomorphy-modified node-based definitions are normally internal (unless external specifiers are used to prevent use of a name under certain hypotheses of relationships, clade composition, or both; see Art. 11.13).
lineage: A series of entities (e.g., organisms, populations) that form a single unbroken and unbranched sequence of ancestors and descendants. That a lineage is unbranched does not deny the existence of side-branches, which are not parts of the lineage in question, or of branching at lower organizational levels (e.g., organelle lineages within a population lineage). There may even be branching at the organizational level in question as long as it is judged to be temporary.
maximum-clade definition: A definition that associates a name with the largest clade that contains one or more internal specifiers but does not contain one or more external specifiers. See Article 9.6.
maximum-crown-clade definition: A definition that associates a name with the largest crown clade that contains one or more internal specifiers but does not contain one or more external specifiers. See Article 9.9.
maximum-total-clade definition: A definition that associates a name with the largest clade that contains one or more internal specifiers but does not contain one or more external specifiers. See Article 9.10.
minimum-clade definition: A definition that associates a name with the smallest clade that contains two or more internal specifiers. See Article 9.5.
minimum-crown-clade definition: A definition that associates a name with the smallest crown clade that contains two or more internal specifiers. See Article 9.9.
monophyletic: A set consisting of an ancestor and all of its descendants; usually used for groups the members of which share a more recent common ancestor with one another than with any non-members, though monophyletic groups of organisms within sexually reproducing species/populations may not have this property.
name: A word or words used to designate (refer to) an organism or a group of organisms. See acceptable name, accepted name, conditionally suppressed name, conserved name, converted name, established name, infraspecific name, new name, panclade name, preexisting name, replacement name, scientific name, specific name, suppressed name, taxon name, typified name, unconditionally suppressed name.
new (clade) name: A newly proposed name that has been established in accordance with the rules of this code (see converted (clade) name).
node: A point or vertex on a tree (in the sense of graph theory). On a phylogenetic tree, a node is commonly used to represent (1) the split of one lineage to form two or more lineages (internal node) or the extinction of a lineage (terminal node) or the lineage at a specified time, often the present (terminal node), or (2) a taxon, whether ancestral (internal node) or descendant (internal node or terminal node).
node-based definition: A term used in earlier versions of this code that is roughly equivalent to a minimum-clade definition in this version (see footnote to Art. 9.5).
nomen cladi conversum: See converted (clade) name.
nomen cladi novum: See new (clade) name.
nomen substitutum: See replacement name.
nominal author: The person(s) who first published a name, regardless whether it was phylogenetically defined (see definitional author).
orthography: The spelling of a name.
panclade name: A name that is derived from the name of a crown clade by the addition of the prefix Pan- and is used to designate the total clade of that crown clade. See Articles 10.3–10.7.
paraphyletic: A set including an ancestor but excluding some or all of its descendants.
phylogenetic: Of or pertaining to the history of ancestry and descent.
phylogenetic definition: A statement specifying a particular clade as the entitiy to which a name refers.
phylogenetic hypothesis (hypotheses): A proposition about the relationships among biological entities (e.g., species, populations, organisms) in terms of common ancestry.
phylogenetic system (of nomenclature): An integrated set of principles and rules governing the naming of taxa and the application of taxon names that is based on the principle of common descent. This code describes a phylogenetic system of nomenclature.
phylogenetic tree: The diagrammatic representation of phylogeny as a tree in the sense of a minimally connected graph (number of branches = number of nodes minus one).
phylogeny: Evolutionary history; the history of descent with modification, whether in general or a particular part thereof. The term is also sometimes used for a hypothesis of phylogenetic relationships (as in the term reference phylogeny).
precedence: The order of preference among established names, used to select the accepted name from among them. In general, precedence is based on the date of establishment, with earlier-established names having precedence over later ones, but later-established names may be conserved over earlier ones.
preexisting name: A scientific name that, prior to its establishment under this code, was either: (a) “legitimate” (ICNAFP, ICNP), “potentially valid” (ICZN), or “valid” (ICVCN); or (b) in use but not governed by any code (e.g., zoological names ranked above the family group).
protologue: Everything associated with a name when it was first established (under this code), validly published (ICNAFP, ICNP), or made available (ICZN), for example, description, diagnosis, phylogenetic definition, registration number, designation of type, illustrations, references, synonymy, geographical data, specimen citations, and discussion.
qualifying clause: A part of a phylogenetic definition that specifies conditions under which the defined name cannot be applied.
rank: The position in a hierarchy; in the case of biological nomenclature, the position in a hierarchy of nested taxa.
rank-based codes: The codes that govern the rank-based system of nomenclature—specifically, the International Code of Nomenclature for Algae, Fungi, and Plants, the International Code of Zoological Nomenclature, the International Code of Nomenclature of Prokaryotes, and the International Code of Virus Classification and Nomenclature.
rank-based system (of nomenclature): An integrated set of principles and rules governing the naming of taxa and the application of taxon names that is based on taxonomic ranks (e.g., kingdom, phylum). Also referred to as the “traditional system.”
reference phylogeny: A phylogenetic hypothesis that provides a context for applying a clade name by means of its phylogenetic definition.
replacement name: A new name explicitly substituted for a previously established name that is not acceptable because it is a later homonym. A replacement name is equivalent to a nomen substitutum in this code. (The term “replacement name” has been used in a broader sense under the ICZN to include what the ICNAFP refers to as a superfluous name and the ICZN refers to as an unnecessary substitute name.)
restricted emendation: A formal change in a phylogenetic definition that requires approval by the Committee on Phylogenetic Nomenclature; a restricted emendation is intended to change the application of a name through a change in the conceptualization of the clade to which it refers. See unrestricted emendation.
scientific name: A taxon name that either is formed and governed by one of the codes of biological nomenclature or is of a similar Latinized form (e.g., zoological names ranked above the family group).
sister clade: One member of a pair of clades originating when a single lineage splits into two. Sister clades thus share an exclusive common ancestry and are mutually most closely related to one another in terms of common ancestry.
species: This term is used both for a kind of biological entity (for example, a population lineage segment) and for the lowest primary rank in traditional nomenclature (and thus also for any taxon assigned to that rank). This code does not endorse any species concept nor provide rules for defining species names, but it uses species names governed by the rank-based codes to refer to taxa that are used as specifiers in definitions of clade names. Article 21 provides guidelines for the use of species names governed by the rank-based codes in conjunction with clade names governed by this code.
specific name: Under the ICZN, the second word in a species binomen.
specifier: A species, specimen, or apomorphy cited in a phylogenetic definition of a name as a reference point that serves to specify the clade to which the name applies.
stem-based definition: A term used in earlier versions of this code that is roughly equivalent to maximum-clade definition in this version (see footnote to Art. 9.5).
stem-modified node-based definition: A term used in earlier versions of this code that is roughly equivalent to a maximum-crown-clade definition in this version (see footnote to Art. 9.5).
suppressed name: A name that would normally have precedence but does not, due to a decision by the Committee on Phylogenetic Nomenclature to give precedence to a later synonym or homonym.
synapomorphy (synapomorphic): A shared apomorphy. In this code, a synapomorphy is a shared, derived character state inherited from a common ancestor that possessed that state; a shared, independently derived character state is not considered to be a synapomorphy in the sense the term is used in this code (see apomorphy).
synonym: A name that is spelled differently than another name that refers to the same taxon. In the case of clade names, synonyms may be homodefinitional or heterodefinitional.
taxon (taxa): A group of organisms or species considered a potential recipient of a scientific name. The only taxa whose names are governed by this code are clades. However, species, whose names are governed by the rank-based codes, are frequently used to define clade names in this code.
taxon name: The word (or, in rank-based codes, words) used to designate a taxon.
taxonomic rank: See categorical rank.
total clade: A clade composed of a crown clade and all organisms (and species) that share a more recent common ancestor with that crown clade than with any extant organisms or species that are not members of that crown clade. See Article 2.2.
total-clade definition: A phylogenetic definition that necessarily identifies a total clade (Art. 2.2) as the referent of a taxon name. See Article 9.10.
type (=nomenclatural type): In the rank-based codes, the specimen, specimens, or subordinate taxon to which a taxon name is permanently attached; the type provides the standard of reference that determines the application of a name.
typified name: A name whose application is determined by a type under a rank-based code.
unconditionally suppressed name: A name that has been suppressed by the Committee on Phylogenetic Nomenclature in all phylogenetic contexts (see suppressed name); there are no conditions under which it would have precedence over any other name.
uninomen (uninomina): A name composed of a single word; in this code, the term is used to refer to the second part of a species binomen that is being treated as the name of a species (though the names of clades are also uninomina).
unrestricted emendation: A formal change in a phylogenetic definition that does not require approval by the Committee on Phylogenetic Nomenclature; an unrestricted emendation is intended to prevent undesirable changes in the application of a particular name (in terms of clade conceptualization) when the original definition is applied in the context of a revised phylogeny. See restricted emendation.