Nomenclature and Taxonomic Hierarchy

The Problem of Instability and Multiplicity of Names

Imagine that you work as an agronomist and in your report you need to indicate the pest that has affected the crops. You write “potato nematode.” Your colleague from another region writes “golden potato nematode.” And in an international database the same organism is listed as Globodera rostochiensis. Confusion arises. It is precisely to solve such problems that scientific nomenclature exists.

The main goal of nomenclature is to ensure stability and universality of scientific names (Turland et al., 2025). This means that each species must have one, and only one, correct scientific name, which is recognized by scientists throughout the world. Without this system, effective communication, data exchange, and reproducibility of research would be impossible (Judd et al., 2018).

The history of systematics knows many examples when the same organism received different names from different researchers or, conversely, the same name was applied to completely different species. Such instability is a real scourge for applied disciplines, including agronomy. For example, the phytopathogenic fungus that causes potato late blight “changed” several names over its history before the generally accepted Phytophthora infestans became fixed for it (Sigee, 1993).

Scientific Name vs. Vernacular Name vs. Commercial Name

To establish order, it is necessary to clearly distinguish between types of names.

1. Vernacular names. These are names used in everyday life. They can be very vivid and convenient in daily life, but they are extremely unreliable for science. For example, “white mushroom” in different regions of Russia may mean different species, and “chamomile” refers to dozens of species from different genera of the family Asteraceae. Vernacular names are not regulated by any rules and cannot serve as the basis for scientific classification (Judd et al., 2018).

2. Commercial names. These are names used in trade for marketing. For example, an apple cultivar may be sold under the name “Gala Schniga,” but its official, registered name as a cultivar will be different. Commercial names are a trademark, not a scientific tool. They are not regulated by biological codes of nomenclature and serve exclusively to attract buyers (Brickell et al., 2016).

3. Scientific (Latinized) names. This is the universal language of biology. A scientific name is assigned to a taxon in accordance with the strict rules of international codes. It does not depend on language, country, or commercial interests. It is scientific names that ensure unambiguous identification of organisms throughout the world.

Nomenclature as the “Legal System” of Biology

Biological nomenclature is often compared to a legal system. And this is a very accurate comparison. We have “codes” (collections of laws), “articles,” and “recommendations.” There are procedures for “registration” of names, “priority” (whoever first gave the name is right), and even a “court” — the International Botanical Congress, which can “cancel” or “conserve” an inconvenient name (Turland et al., 2025).

This “legal” strictness is necessary because science is a collective process. In order for the results of one researcher to be used by others, there must be confidence that everyone is talking about the same objects. Nomenclature provides this tool. For example, when you read that Triticum aestivum L. is affected by Puccinia graminis Pers., you can be sure that the text refers to common wheat and stem rust, regardless of what language the author of the study speaks.

In the following sections, we will examine in detail how these “laws” — international codes — are structured, what key concepts they use, and how this system helps scientists and practitioners throughout the world.

ICN (International Code of Nomenclature for algae, fungi, and plants)

This code, whose full name is International Code of Nomenclature for algae, fungi, and plants, is the main document for botanists, mycologists, and algologists. It regulates the names of all organisms traditionally studied as plants, fungi, and algae, including cyanobacteria (Judd et al., 2018). The latest edition to date is the Madrid Code of 2025, adopted at the XX International Botanical Congress in Madrid (Turland et al., 2025).

For specialists in the agricultural sphere, this code is of primary importance, since it determines the names of all cultivated plants, their wild relatives, as well as phytopathogenic fungi and fungus-like organisms. For example, the names of such important genera as Triticum (wheat), Solanum (nightshade, including potato and tomato), and Phytophthora (the causative agent of late blight) are regulated precisely by ICN.

A key feature of ICN that is important to remember is its retroactivity. This means that the rules of the code apply to all names published after 1 May 1753 (the date of publication of Carl Linnaeus’s Species Plantarum), even if at that time these rules did not yet exist (Turland et al., 2025).

ICZN (International Code of Zoological Nomenclature)

Zoologists have their own code — the International Code of Zoological Nomenclature (ICZN), or the International Code of Zoological Nomenclature (Ride et al., 1999). It regulates the names of all animals, from insect pests to agricultural animals. Although within our course we do not go deeply into zoology, it is important to understand that the principles of this code are in many ways similar to ICN, but also have significant differences.

For example, the starting point for zoological nomenclature is 1 January 1758, also connected with Linnaeus’s work, but with the 10th edition of Systema Naturae. In addition, ICZN has its own unique rules concerning, for example, the designation of authorship and typification (ICZN, 1999).

For the agricultural sphere, knowledge of ICZN is important when it concerns pests — insects, mites, nematodes. For example, the name of the Colorado potato beetle — Leptinotarsa decemlineata (Say, 1824) — is regulated precisely by this code. If you work with entomopathogenic nematodes, their names are also subject to ICZN.

ICTV (International Committee on Taxonomy of Viruses)

Viruses are a special group that falls under neither botanical nor zoological codes. For them, there exists the International Committee on Taxonomy of Viruses (ICTV), which develops and maintains a unified system of classification and nomenclature of viruses (King et al., 2012).

ICTV’s approach to nomenclature differs substantially from ICN and ICZN. For example, ICTV not only regulates the rules for assigning names but also approves the creation of the taxa themselves (species, genera, families). Priority of publication here is not a determining factor. Taxon names are written in italics with a capital letter, and species names are often formed from English vernacular names of viruses (King et al., 2012).

For an agronomist this is critically important, since many plant diseases have a viral nature. For example, Tomato mosaic virus, Potato leafroll virus — all these names are regulated by ICTV. Understanding ICTV rules is necessary for correct work with viral pathogens and their identification in scientific literature and databases.

ICNP (International Code of Nomenclature of Prokaryotes)

For completeness, one more code should be mentioned — the International Code of Nomenclature of Prokaryotes (ICNP), which regulates the names of bacteria and archaea (Parker et al., 2019). In the agricultural sphere, this is important for work with phytopathogenic bacteria such as Erwinia amylovora (the causative agent of fire blight of fruit crops), Agrobacterium tumefaciens (the causative agent of crown gall), and many others.

Although we will not analyze ICNP in detail within this course, it is important to know of its existence. Bacterial names are also Latinized, written in italics, and have their own rules of author citation. For example, Pseudomonas syringae van Hall 1902 is a full name with author and year, which is regulated by ICNP.

Principles Common to All Codes

Despite differences, all codes are based on several fundamental principles that ensure the stability and universality of nomenclature.

1. Independence of codes. This principle means that the nomenclature of different groups of organisms is independent. A name given to an animal cannot be rejected merely because it coincides with the name of a plant. For example, the genus Pieris exists both among insects (white butterflies) and among plants (shrubs of the family Ericaceae). This is not an error but a consequence of the independence of the codes (Judd et al., 2018). Moreover, a name given to an organism under one code is not “automatically” transferred to another. If a species was described as an animal and later assigned to plants, its name must be checked for compliance with ICN and, if necessary, changed.

2. Principle of priority. This is perhaps the most important principle. It states: the correct name of a taxon is the earliest published name that corresponds to the rules of the code (Turland et al., 2025). If the same species was described by different authors under different names, then the one published earlier will be the correct one. This prevents chaos and ensures predictability. However, there are exceptions to this rule, for example, the procedure of conservation of names, which we will discuss later (Turland et al., 2025).

3. Principle of typification. In order for a name to be reliably tied to a specific biological object, each taxon of species or genus rank has a nomenclatural type. This is not necessarily the most typical representative, but the specific specimen (herbarium sheet, preparation, culture) with which the name is forever associated. Typification is the procedure for designating such a specimen. Without this principle, the name could “float” between different understandings of the taxon. We will discuss types in more detail in the next section (Turland et al., 2025).

4. Latinized names. Scientific names of taxa must be in Latin or Latinized, regardless of their origin. This ensures their universality and independence from modern languages. Even if a name originates from a Russian word, it must be formatted according to the rules of Latin grammar. For example, the name of the genus Larix (larch) is a Latin word, and Picea (spruce) comes from the Latin pix (resin) (Judd et al., 2018).

Binary Nomenclature: Genus + Specific Epithet

The basis of modern biological nomenclature is binary nomenclature — a system introduced by Carl Linnaeus in the 18th century. According to this system, the scientific name of a species consists of two words (Judd et al., 2018).

1. Generic name. This is a noun in the singular, which is written with a capital letter and always in italics. It denotes a group of closely related species. For example, Triticum — the genus wheat, Solanum — the genus nightshade, Quercus — the genus oak.

2. Specific epithet. This is the second word in the name, which is written with a lowercase letter and also always in italics. It is not an independent name and is not used separately from the generic name. For example, in the name Triticum aestivum (common wheat), the specific epithet is aestivum (summer). In the name Solanum tuberosum (potato), the specific epithet is tuberosum (tuberous).

It is important to understand that the specific epithet is not merely an adjective describing a trait. It may be:

• an adjective agreeing in gender with the generic name (Solanum tuberosum — neuter);
• a noun in the nominative case (in apposition), for example, Ficus religiosa (sacred fig);
• a noun in the genitive case, often formed from a person’s name or a geographical name, for example, Quercus virginiana (Virginia oak) or Magnolia chapensis (Chap’s magnolia).

The full name of a species, including the generic name and specific epithet, is called a binomen (Turland et al., 2025). It is the binomen that serves as the unique identifier used in scientific literature.

For infraspecific taxa (subspecies, varieties, forms), a trinomen is used — a name consisting of three words: the generic name, the specific epithet, and the epithet of the infraspecific taxon. For example, Triticum aestivum subsp. spelta — common wheat subspecies spelt. In this case, the third word (spelta) is also written in italics with a lowercase letter.

Author of the Name, Year of Publication, Parentheses

In scientific literature, it is customary to indicate the author of the name and the year of its publication. This helps to accurately identify which taxon is being discussed and to trace the history of the name. The rules of author citation differ for plants and animals, but the general principles are similar.

For plants (ICN):

The author of the name is indicated after the binomen without a comma. For example, Zea mays L. — the name of maize given by Linnaeus (L. is the standard abbreviation for Linnaeus). Phytophthora infestans (Mont.) de Bary — the causative agent of late blight. Here we see parentheses: (Mont.) means that this species was originally described by Montagne under a different generic name, and then de Bary transferred it to the genus Phytophthora. The parentheses indicate that the author of the species name is de Bary, but the basionym (the original name) was given by Montagne (Turland et al., 2025).

If the author of the name did not change when transferred to another genus, parentheses are not used. For example, Puccinia graminis Pers. — the causative agent of stem rust, described by Persoon and remaining in the same genus.

The year of publication may be indicated after the author, but this is not obligatory. For example, Zea mays L., 1753 or simply Zea mays L.

For animals (ICZN):

In zoological nomenclature, the author and year are indicated after the name, often separated by a comma. For example, Leptinotarsa decemlineata (Say, 1824) — the Colorado potato beetle. Parentheses here also mean that the species was originally described in another genus (ICZN, 1999).

Unlike botany, in zoology the year of publication is often indicated, and this is a stricter rule. Author abbreviations for zoologists are also standardized.

For bacteria (ICNP):

In bacteria, the author and year are also indicated after the name. For example, Erwinia amylovora (Burrill, 1882) Winslow et al., 1920. Here we see a more complex construction: the original name was given by Burrill in 1882, and then Winslow and colleagues in 1920 transferred it to the genus Erwinia. The parentheses indicate the original author, and after the parentheses is the author of the new combination (Parker et al., 2019).

Synonyms, Basionyms, Homonyms

In systematics, situations often arise when the same taxon has several names. Special terms are used to describe such situations.

Synonyms are different names applied to the same taxon. According to the principle of priority, the correct one is the earliest of them. The remaining names become synonyms. For example, Puccinia graminis Pers. is the correct name of stem rust. Puccinia graminis f. sp. tritici is a special form, which is also used, but is not a separate species. Synonyms may be:

• homotypic (nomenclatural) — based on the same type;
• heterotypic (taxonomic) — based on different types, but recognized as belonging to the same taxon as a result of taxonomic revision (Turland et al., 2025).

Basionym is the original name on which a new name is based. For example, when the species Montagnea was transferred to the genus Phytophthora, the basionym is Montagnea infestans Mont. The new name is Phytophthora infestans (Mont.) de Bary. The basionym is always indicated in parentheses in author citation (Turland et al., 2025).

Homonyms are names identical in spelling given to different taxa. According to the principle of homonymy, the younger homonym (later in time of publication) cannot be used and must be replaced. For example, if the genus Pieris exists both among plants and among animals, this is not homonymy, since the codes are independent. But if two different genera of plants received the same name, the later one must be replaced (Turland et al., 2025). Homonyms may be:

• primary — when identical names were given to different taxa initially;
• secondary — when different names become identical as a result of transfer to one genus.

Types: Holotype, Lectotype, Neotype, Epitype

The principle of typification is one of the cornerstones of nomenclature. Each name of a species or genus must be tied to a specific nomenclatural type — a specimen that serves as the standard for applying the name. The type is not necessarily the most typical representative, but the specific object with which the name is inextricably linked (Turland et al., 2025).

Several categories of types are distinguished:

1. Holotype — the single specimen indicated by the author when describing a new species. This is the main type, which is stored in a herbarium or collection. For example, the holotype of Triticum aestivum L. is stored in Linnaeus’s herbarium in London.

2. Lectotype — a specimen selected from the original material (syntypes) later, if a holotype was not designated or has been lost. Lectotypification is a procedure that allows stabilizing the application of a name if the original material is heterogeneous (Turland et al., 2025).

3. Neotype — a specimen selected as the type if all the original material has been lost or destroyed. Neotypification is also used to stabilize names (Turland et al., 2025).

4. Epitype — a specimen selected to clarify the application of a name when the holotype, lectotype, or neotype is insufficient for identification (for example, poorly preserved or not showing diagnostic characters). The epitype does not replace the main type but supplements it (Turland et al., 2025).

For genera and families, the type is the type species or type genus, respectively. For example, the type of the genus Triticum is Triticum aestivum L., and the type of the family Poaceae is the genus Poa L. (Turland et al., 2025).

Effective and Valid Publication

In order for a name to be recognized by the scientific community, it must be effectively published and validly published. These two concepts are often confused, but they have different meanings.

Effective publication means that the name was disseminated in printed form (or in electronic form since 2012) among the scientific public. This may be a journal, book, or monograph. Names published in manuscripts, on herbarium specimen labels, in oral presentations, or on the internet without compliance with formal requirements are not considered effectively published (Turland et al., 2025).

Valid publication is a stricter concept. In order for a name to be validly published, it must meet a number of requirements:

• be effectively published;
• have a description or diagnosis in Latin (for plants published before 2012) or in Latin or English (since 2012);
• be accompanied by an indication of the type (for species and genera published after certain dates);
• be published in accordance with the rules of the code (Turland et al., 2025).

If a name is not validly published, it has no nomenclatural force and cannot compete for priority. For example, nomina nuda (names published without a description) are not validly published and are invalid.

Why a Name May Change upon Revision of Systematics

One of the most frequent reasons for changes in names is taxonomic revision. When scientists conduct molecular phylogenetic studies, they may discover that traditional genera or species are not monophyletic groups. As a result, taxa are revised, and names may change.

For example, the genus Fusarium is a large genus of fungi including many phytopathogenic species. Molecular studies have shown that some species traditionally assigned to Fusarium actually belong to other genera. As a result, new genera were described, such as Gibberella (the teleomorph of Fusarium) and others. Species names were revised, and new combinations are now used for many pathogens (Webster & Weber, 2007).

Another example is the reorganization of the family Scrophulariaceae (figworts). Based on molecular data, many genera were transferred to other families, such as Plantaginaceae (plantains) and Orobanchaceae (broomrapes). For example, the genus Verbascum (mullein) remained in Scrophulariaceae, while the genus Digitalis (foxglove) was transferred to Plantaginaceae (Judd et al., 2018). This led to changes in the names of many species.

Understanding the reasons for changes in names is important for practical work. When you encounter a new name in the literature, it is not always an error or “renaming for the sake of renaming.” Often it is the result of serious scientific research aimed at creating a more natural classification.

Section Conclusion

Basic nomenclatural concepts are the tools that allow us to work with taxon names consciously and correctly. Binary nomenclature gives us a universal language, author citation gives precision, synonymy and typification give stability, and understanding the processes of revision gives flexibility. In the next section, we will move on to taxonomic hierarchy and consider how these concepts are applied to ranks — from species to kingdom.

Main Ranks: Species → Genus → Family → Order → Class → Division/Phylum → Kingdom/Domain

Taxonomic hierarchy is a system of subordinate categories (ranks) into which taxa are placed. Each taxon of a lower rank is included in a taxon of a higher rank. This system was first consistently applied by Carl Linnaeus in the 18th century and has since been called the Linnaean hierarchy (Judd et al., 2018; Stuessy, 2009).

The main ranks, from lowest to highest, are as follows:

1. Species. This is the basic rank in biological classification. As we have already said, a species is a set of populations capable of interbreeding and possessing common morphological, physiological, and genetic characters (Pandey & Kasana, 2021). The species is the unit with which agronomists, phytopathologists, and ecologists most often work. For example, Triticum aestivum is a species, Solanum tuberosum is a species.

2. Genus. This is the next rank above species. A genus unites closely related species that have a common origin and a number of common characters. The name of the genus is the first word in the binomen. For example, the genus Triticum unites several species of wheat, the genus Solanum — many species of nightshades, including potato and tomato.

3. Family. A rank uniting close genera. Names of families in plants are formed by adding the standard ending -aceae to the stem of the name of the type genus. For example, the family Poaceae (grasses) is formed from the genus Poa, the family Solanaceae (nightshades) — from the genus Solanum, the family Asteraceae (asters) — from the genus Aster (Turland et al., 2025). In animals, family names are formed with the ending -idae, for example, Coccinellidae (ladybirds) from the genus Coccinella (ICZN, 1999).

4. Order. A rank uniting close families. Names of orders in plants have the standard ending -ales (for example, Poales, Solanales, Asterales) (Turland et al., 2025). In animals — -iformes (for example, Coleoptera — beetles, although this is an order, not an order in the botanical sense, but the ending is similar). In botany, orders are often named after the type family. For example, the order Poales includes the families Poaceae, Cyperaceae, Juncaceae, and others.

5. Class. A rank uniting orders. In plants, class names have the ending -opsida (for example, Liliopsida — monocots, Magnoliopsida — dicots) (Turland et al., 2025). In animals — -ia or others. For example, the class Insecta (insects), the class Mammalia (mammals) (ICZN, 1999).

6. Division or phylum. In botany the term “division” is used, in zoology — “phylum.” This is a very high rank uniting classes. In plants, division names have the ending -phyta (for example, Magnoliophyta — angiosperms, Pinophyta — gymnosperms) (Turland et al., 2025). In animals, for example, the phylum Arthropoda (arthropods), the phylum Chordata (chordates) (ICZN, 1999).

7. Kingdom. The highest rank in the traditional hierarchy. Kingdoms Plantae (plants), Animalia (animals), Fungi (fungi), Bacteria (bacteria), and others are distinguished (Judd et al., 2018).

8. Domain. This rank was introduced relatively recently, in the 1990s, based on molecular data. It is above kingdom. Three domains are distinguished: Bacteria (eubacteria), Archaea (archaea), and Eukarya (eukaryotes, including plants, animals, fungi, and protists) (Judd et al., 2018; Woese et al., 1990).

Thus, the hierarchy looks like this (from highest to lowest):

Domain → Kingdom → Division/Phylum → Class → Order → Family → Genus → Species

Each taxon of a lower rank is necessarily included in a taxon of a higher rank. For example, the species Triticum aestivum is included in the genus Triticum, which is included in the family Poaceae, which is included in the order Poales, which is included in the class Liliopsida, which is included in the division Magnoliophyta, which is included in the kingdom Plantae.

For illustration, let us give an example of a complete hierarchy for a well-known object — maize (Zea mays L.):

• Domain: Eukarya
• Kingdom: Plantae
• Division: Magnoliophyta (angiosperms)
• Class: Liliopsida (monocots)
• Order: Poales (grasses)
• Family: Poaceae (grasses)
• Genus: Zea
• Species: Zea mays L.

A similar example for an animal — the Colorado potato beetle (Leptinotarsa decemlineata):

• Domain: Eukarya
• Kingdom: Animalia
• Phylum: Arthropoda (arthropods)
• Class: Insecta (insects)
• Order: Coleoptera (beetles)
• Family: Chrysomelidae (leaf beetles)
• Genus: Leptinotarsa
• Species: Leptinotarsa decemlineata (Say, 1824)

Additional Ranks: Sub-, Super-, Infra-; Tribe, Section, Series, Variety, Form

The main ranks are often insufficient to reflect all nuances of phylogenetic relationships. Therefore, additional ranks are used, which are formed by adding the prefixes sub-, super-, and infra- to the main ranks (Turland et al., 2025; ICZN, 1999).

For example:

• Subspecies — a rank below species. Designated as subsp. or ssp.
• Variety — a rank below subspecies. Designated as var.
• Form — a rank below variety. Designated as f.
• Subgenus — a rank below genus.
• Superfamily — a rank above family but below order.
• Subfamily — a rank below family.
• Tribe — a rank between family and genus. In plants, tribes are often used to group genera within large families, for example, in the family Asteraceae tribes Astereae, Cichorieae, and others are distinguished (Judd et al., 2018).
• Section — a rank between genus and species, used to group closely related species within large genera. For example, in the genus Solanum sections Solanum sect. Solanum, Solanum sect. Lycopersicon, and others are distinguished (Turland et al., 2025).
• Series — a rank below section.

The hierarchy with additional ranks can look very complex. For example, for plants the following sequence is possible: kingdom → subkingdom → division → subdivision → class → subclass → superorder → order → suborder → superfamily → family → subfamily → tribe → subtribe → genus → subgenus → section → subsection → series → subseries → species → subspecies → variety → subvariety → form → subform (Turland et al., 2025).

In practice, in the agricultural sphere the following infraspecific ranks are most often used:

• Subspecies: for example, Triticum aestivum subsp. spelta — common wheat subspecies spelt.
• Variety: for example, Beta vulgaris var. conditiva — garden beet.
• Form: for example, Lactuca sativa f. crispa — leaf lettuce.

For cultivated plants, in addition to these ranks, there are special categories, which we will consider below.

Examples for Plants, Animals, Bacteria, Viruses

Taxonomic hierarchy is universal, but its application has features for different groups of organisms.

Plants (ICN):

• Species: Triticum aestivum L. (common wheat)
• Genus: Triticum L.
• Family: Poaceae Barnhart (grasses)
• Order: Poales Small (grass order)
• Class: Liliopsida Batsch (monocots)
• Division: Magnoliophyta Cronquist, Takht. & W.Zimm. (angiosperms)
• Kingdom: Plantae Haeckel (plants)

Animals (ICZN):

• Species: Leptinotarsa decemlineata (Say, 1824) (Colorado potato beetle)
• Genus: Leptinotarsa Stål, 1858
• Family: Chrysomelidae Latreille, 1802 (leaf beetles)
• Order: Coleoptera Linnaeus, 1758 (beetles)
• Class: Insecta Linnaeus, 1758 (insects)
• Phylum: Arthropoda Latreille, 1829 (arthropods)
• Kingdom: Animalia Linnaeus, 1758 (animals)

Bacteria (ICNP):

• Species: Erwinia amylovora (Burrill, 1882) Winslow et al., 1920 (causative agent of fire blight of fruit crops)
• Genus: Erwinia Winslow et al., 1917
• Family: Erwiniaceae Adeolu et al., 2016
• Order: Enterobacterales Adeolu et al., 2016
• Class: Gammaproteobacteria Garrity et al., 2005
• Phylum: Proteobacteria Stackebrandt et al., 1988
• Kingdom: Bacteria (eubacteria)

Viruses (ICTV):

• Species: Tomato mosaic virus
• Genus: Tobamovirus
• Family: Virgaviridae
• Order: Martellivirales (King et al., 2012)

As we can see, in viruses the hierarchy does not always reach class and phylum, since their classification is in a stage of active development, and ICTV approves only those taxa that are well substantiated.

For Cultivated Plants: ICNCP, Cultivar, Group, Grex

Cultivated plants are a special category of organisms that arose as a result of deliberate selection and often have no analogues in nature. For their nomenclature there is a separate code — the International Code of Nomenclature for Cultivated Plants (ICNCP), or International Code of Nomenclature for Cultivated Plants (Brickell et al., 2016). The latest edition is the 9th, published in 2016.

ICNCP regulates the names of cultivars, Groups, and greges. It is important to understand that these categories are not taxonomic ranks in the strict sense, but represent special categories for classifying plants that arose in cultivation.

1. Cultivar — a set of plants that has been selected for a particular character or set of characters, remains distinguishable, uniform, and stable when propagated by appropriate methods (Brickell et al., 2016). The name of a cultivar consists of the name of the genus or species and the cultivar epithet, which is enclosed in single quotation marks and is not italicized. For example, Malus domestica 'Antonovka' — a cultivar of the domestic apple, Solanum tuberosum 'Udacha' — a cultivar of potato.

Important: the abbreviation cv. (cultivar) before the epithet has not been used since 1996. It is correct to write: Triticum aestivum 'Mironovskaya 808', not Triticum aestivum cv. Mironovskaya 808 (Brickell et al., 2016).

2. Group — a category uniting cultivars, individual plants, or their assemblages on the basis of a certain similarity (Brickell et al., 2016). The name of a Group consists of the name of the genus or species and the Group epithet, which includes the word “Group” (or its equivalent in other languages). For example, Brassica oleracea Gemmifera Group — Brussels sprout Group, Rosa Polyantha Group — polyantha rose Group.

3. Grex — a category used only in orchid nomenclature to designate the progeny from a particular crossing (Brickell et al., 2016). The name of a grex consists of the genus name and the grex epithet, followed by the word “grex” or the abbreviation “gx.” For example, Paphiopedilum Sorel grex.

These categories allow systematizing the enormous diversity of cultivated plants created by humans and ensure the stability of their names in agricultural practice and trade.

For Animals: Breed, Line, Cross — Not Taxonomic Ranks

In animal husbandry there are also categories for classifying domestic animals, but it is important to understand that they are not taxonomic ranks in the sense of ICZN. Breed, line, and cross are categories used in animal science and breeding, not in biological systematics.

• Breed — a group of domestic animals of one species possessing common characters and stably transmitting them to offspring. For example, the Holstein cattle breed, the Landrace pig breed.
• Line — a group of animals descending from one outstanding sire or group of sires, possessing certain economically useful characters.
• Cross — the progeny from crossing two different lines or breeds.

Names of breeds and lines are not regulated by ICZN and are not italicized. They are part of agricultural practice, not biological nomenclature. However, when working with pests and pathogens that are wild species, it is necessary to apply ICZN and use scientific names.

Clade Is an Evolutionary Branch, Rank Is a Formal Step of Hierarchy

Let us begin with definitions.

Clade (from Greek klados — branch) is a group of organisms including a common ancestor and all its descendants. A clade is a natural, objectively existing group reflecting real relationships that existed in the history of life on Earth (Judd et al., 2018; Simpson, 2015). A clade exists regardless of whether we know about it or not, and regardless of whether we have assigned any rank to it.

Clades are nested within each other like matryoshka dolls. For example, all angiosperms (flowering plants) form one large clade. Within it there is the clade of monocots, within monocots — the clade of grasses (Poaceae), within grasses — the clade of the genus Triticum (wheat), within it — the clade of the species Triticum aestivum (common wheat). This nesting reflects the sequence of evolutionary events: first the branch leading to angiosperms diverged, then to monocots, then to grasses, and so on (Judd et al., 2018).

Taxonomic rank is a formal step in the Linnaean hierarchy: species, genus, family, order, class, division, kingdom. Rank is a human construct, a conventional “shelf” onto which we place a taxon in order to organize knowledge about it (Stuessy, 2009). Rank does not exist in nature; it is a tool of our classification, our agreement about how to name groups of different levels of inclusiveness.

The key idea: a clade is what exists in nature, while a rank is what we ascribe to a clade in our classification. The same clade in different classification systems may have different ranks, and different clades may have the same rank (Judd et al., 2018; Stuessy, 2009).

Why Monophyletic Groups Do Not Always Coincide with Traditional Ranks

Modern systematics strives for all recognized taxa to be monophyletic, that is, to correspond to clades. However, historically established taxa are far from always monophyletic. Many traditional ranks (families, genera, orders) were distinguished on the basis of morphological similarity which, as molecular phylogenetic studies have shown, may be the result of convergence or parallelism, rather than common descent (Simpson, 2015).

Let us give several examples.

Example 1: Angiosperms and APG IV

The traditional system of classification of flowering plants, for example, the Cronquist system (Cronquist, 1981), divided them into two classes: dicots (Magnoliopsida) and monocots (Liliopsida). However, molecular data showed that “dicots” are not a clade but a paraphyletic group: monocots arose from ancient dicots, but are not included in the class Magnoliopsida (Judd et al., 2018; APG IV, 2016). Thus, the traditional class “dicots” does not correspond to any clade.

In the APG IV system (Angiosperm Phylogeny Group IV, 2016), which is the result of a collective analysis of molecular data, the division into “dicots” and “monocots” as formal classes was abandoned. Instead, clades are recognized: monocots (a monophyletic group), eudicots (a monophyletic group within the former “dicots”), as well as a number of smaller basal groups (Judd et al., 2018; APG IV, 2016). For example, the family Nymphaeaceae (water lilies) and Magnoliaceae (magnolias) belong to basal angiosperms and are included neither in monocots nor in eudicots.

Example 2: The family Liliaceae (lilies)

Traditionally, the family Liliaceae was understood very broadly and included many genera with bulbs, linear leaves, and trimerous flowers: lilies, tulips, onions, hyacinths, asparagus, lily of the valley, and many others. Molecular studies showed that this is a composite group consisting of several independent evolutionary lineages that do not form a single clade (Judd et al., 2018; APG IV, 2016).

As a result, the family was divided into many smaller monophyletic families: Liliaceae s.s. (lilies in the narrow sense, including Lilium, Tulipa, Fritillaria), Alliaceae (onions), Asparagaceae (asparagus), Hyacinthaceae (hyacinths), Convallariaceae (lily of the valley), and others. Each of these families corresponds to a separate clade (Judd et al., 2018; APG IV, 2016). This is an example of how a traditional rank (family) did not coincide with a clade, and reorganization was required.

Example 3: Fungi and pseudofungi

Even more dramatic changes occurred in the systematics of fungi. Traditionally, fungi were considered a single group of organisms, but molecular data showed that “fungi” in the broad sense are several independent evolutionary lineages that are not even close relatives (Webster & Weber, 2007; Sokirko & Gorkovenko, 2019).

Oomycetes (Oomycota), to which the causative agent of late blight Phytophthora infestans belongs, were previously considered fungi. However, their cell walls contain cellulose rather than chitin, and molecular data placed them in a separate kingdom Chromista (or Straminipila) (Webster & Weber, 2007; Sokirko & Gorkovenko, 2019). Thus, “fungi” in the old understanding are a polyphyletic group that does not correspond to any clade.

The modern system (for example, in the 9th edition of Ainsworth & Bisby's Dictionary of the Fungi) divides fungi and fungus-like organisms into three kingdoms: Chromista (pseudofungi), Protozoa (slime molds), and Fungi (true fungi) (Sokirko & Gorkovenko, 2019). For an agronomist this is of enormous practical importance: disease agents that were previously considered fungi may now belong to different kingdoms, which affects the choice of methods for controlling them.

Example 4: Bacteria and archaea

Until the 1970s, all prokaryotes (organisms without a formed nucleus) were united in one kingdom Monera. Carl Woese and his colleagues, based on comparison of ribosomal RNA sequences, showed that prokaryotes are divided into two fundamentally different groups: Bacteria (eubacteria) and Archaea (archaea), which diverged very long ago and have fundamental biochemical differences (Woese et al., 1990; Judd et al., 2018).

Moreover, archaea turned out to be closer to eukaryotes than to bacteria. As a result, a three-domain system was proposed: Bacteria, Archaea, and Eukarya. The kingdom Monera was abolished as not corresponding to any clade (Woese et al., 1990; Judd et al., 2018). For the agricultural sphere this is important because phytopathogenic bacteria (for example, Erwinia amylovora) belong to the domain Bacteria, and their names are regulated by ICNP.

These examples show that taxonomic ranks are merely labels that we attach to clades for convenience. When new data show that a traditional rank does not correspond to a clade, the system is revised. This is not “renaming for the sake of renaming,” but bringing classification into correspondence with evolutionary history.

Examples: APG IV for Angiosperms, Rearrangements in the Systematics of Fungi and Bacteria

Let us consider in more detail how these principles are implemented in modern classifications.

APG IV (2016)

The APG IV system is the result of the work of an international group of botanists who summarized molecular phylogenetic data on all angiosperms. In this system:

• 64 orders and 416 families are recognized (APG IV, 2016).
• The traditional division into “dicots” and “monocots” as formal classes was abandoned; instead, clades are distinguished: monocots, eudicots, superrosids, superasterids, and a number of basal groups (APG IV, 2016; Judd et al., 2018).
• Many families were revised. For example, the family Scrophulariaceae (figworts) was divided: the genera Digitalis (foxglove), Plantago (plantain), and Veronica (speedwell) were transferred to Plantaginaceae (plantains), while the genera Orobanche (broomrape) and Striga (witchweed) — to Orobanchaceae (broomrapes) (APG IV, 2016; Judd et al., 2018).
• The family Lamiaceae (mints) was expanded by including many genera previously assigned to Verbenaceae (vervains), which turned out to be paraphyletic (APG IV, 2016).

For an agronomist this means that when working with scientific literature it is necessary to use modern names of families and genera. For example, if you encounter the name Digitalis purpurea L. in old literature, it may be indicated as a member of the family Scrophulariaceae, but in the modern system it is Plantaginaceae.

Rearrangements in the systematics of fungi

As already mentioned, fungi in the broad sense were divided into three kingdoms. Within the kingdom Fungi (true fungi), significant changes also occurred. For example:

• The division Zygomycota (zygomycetes) was recognized as polyphyletic and divided into several divisions: Mucoromycota, Zoopagomycota, and others (Sokirko & Gorkovenko, 2019; Webster & Weber, 2007).
• The division Chytridiomycota (chytrids) was also revised; some groups were separated into distinct divisions, for example, Blastocladiomycota (Sokirko & Gorkovenko, 2019).
• Genera previously assigned to Fusarium were revised: teleomorphs (sexual stages) were assigned to the genera Gibberella and Nectria, while anamorphs (asexual stages) remained in Fusarium (Webster & Weber, 2007).

These changes are important for phytopathologists, since the names of disease agents may change. For example, the causative agent of Fusarium wilt may be indicated as Fusarium oxysporum (anamorph) or Gibberella sp. (teleomorph), depending on the stage of the life cycle and the context.

Rearrangements in the systematics of bacteria

In the systematics of bacteria, significant changes have also occurred. For example:

• The genus Erwinia was divided into several genera: Erwinia s.s., Pectobacterium, Dickeya, and Brenneria (Sigee, 1993). This is important for phytopathologists, since different species of these genera cause different diseases: Erwinia amylovora — fire blight of fruit crops, Pectobacterium carotovorum — soft rot of vegetables.
• The genus Pseudomonas was divided into several genera, including Pseudomonas s.s., Burkholderia, Ralstonia, and Acidovorax (Sigee, 1993). For example, the causative agent of bacterial wilt of tomato Ralstonia solanacearum was previously called Pseudomonas solanacearum.

These changes reflect the refinement of phylogenetic relationships based on molecular data. For practical work, this means the need to track modern names and use them in diagnostics and plant protection.

Why Different Databases (NCBI, GBIF, Tropicos) Use Different Ranks and Names

One of the practical problems encountered by specialists in the agricultural sphere is the diversity of names and ranks in different databases. Why does this happen?

There are several reasons:

1. Different data sources. Databases such as NCBI (GenBank), GBIF (Global Biodiversity Information Facility), Tropicos, Index Fungorum, MycoBank, and others use different sources for their content. Some databases are oriented toward molecular data (NCBI), others toward taxonomic revisions (Tropicos), and still others toward biodiversity (GBIF). Each database may follow its own classification, which may lag behind the latest publications or, conversely, be ahead of them (Watson, 2015).

2. Different taxonomic concepts. Different authors may adhere to different concepts of species, genus, or family. For example, some researchers may recognize a broad genus Fusarium, while others divide it into several narrower genera. This leads to the fact that the same name in different databases may designate different taxa, or the same taxon may have different names (Watson, 2015).

3. Update lag. Even if a new classification has been published in the scientific literature, databases may update with a delay. This is especially characteristic of large databases that aggregate data from many sources. As a result, an outdated name may remain in the database (Watson, 2015).

4. Absence of a single standard. Although international codes exist, they regulate the rules for assigning names but do not prescribe which taxa must be recognized. For example, there is no single “law” that would oblige everyone to recognize the family Liliaceae in the narrow or broad sense. This is a matter of scientific consensus and taxonomic practice (Watson, 2015).

For an agronomist this means that when working with databases it is necessary to:

• Indicate the data source and date of access.
• Check the relevance of names in several sources, if possible.
• Be prepared for the fact that the same name may have different meanings in different databases.
• Use unique identifiers (for example, GUID, LSID) for unambiguous identification of taxa, if the database provides them (Watson, 2015).

Italics for Generic and Specific Names. Capital Letter Only for the Genus

The very first and most important rule: scientific names of genera, species, and infraspecific taxa are written in italics. This applies to binomens and trinomens. For example:

• Triticum aestivum (common wheat)
• Solanum tuberosum (potato)
• Phytophthora infestans (causative agent of late blight)
• Leptinotarsa decemlineata (Colorado potato beetle)

Italics are a typographic way of showing that we are dealing with a scientific name rather than an ordinary word. In handwritten texts or when italics cannot be used, underlining is permitted, but in modern publications this is practically not used (Judd et al., 2018; Turland et al., 2025).

The second rule: the generic name is always written with a capital letter, the specific epithet — always with a lowercase letter. Even if the specific epithet is formed from a proper name or a geographical name, it is written with a lowercase letter. For example:

• Magnolia chapensis (Chap’s magnolia) — the specific epithet chapensis with a lowercase letter, although it comes from a place name.
• Quercus virginiana (Virginia oak) — virginiana with a lowercase letter.
• Escherichia coli (E. coli) — coli with a lowercase letter.

This rule is universal for all codes. It helps visually distinguish the generic name from the specific epithet and correctly understand the structure of the binomen (Turland et al., 2025; ICZN, 1999; Parker et al., 2019).

For infraspecific taxa (subspecies, varieties, forms), the third word is also written in italics and with a lowercase letter. For example: Triticum aestivum subsp. spelta (common wheat subspecies spelt), Beta vulgaris var. conditiva (garden beet). Rank designations (subsp., var., f.) are written in roman type, not italics (Turland et al., 2025).

Abbreviating the Genus after First Mention: Triticum aestivum → T. aestivum

In scientific texts, especially when the same genus is mentioned repeatedly, it is customary to abbreviate the generic name to the first letter (or several letters) after the first full mention. For example:

• First mention: Triticum aestivum L.
• Subsequent mentions: T. aestivum.

This rule saves space and facilitates reading, but requires caution. The abbreviation must be unambiguous. If the text contains several genera beginning with the same letter, the abbreviation may lead to confusion. In such cases it is recommended to use a longer abbreviation or not to abbreviate at all. For example, if an article mentions Triticum and Trifolium, the abbreviation T. will be ambiguous. It is better to write Triticum and Trifolium in full or use Trit. and Trif. (Judd et al., 2018; Stuessy, 2009).

At the first mention in the text, it is desirable to give the full name with the author, and subsequently one may use the abbreviated name without the author. For example: “The experiments used Triticum aestivum L. (common wheat). Plants of T. aestivum were grown under controlled conditions...” (Turland et al., 2025).

For viruses there are also standard abbreviations, but they are not obligatory and must be expanded at first mention. For example, Tomato mosaic virus (ToMV). However, in official ICTV nomenclature it is recommended to use full names, and abbreviations only for convenience (King et al., 2012).

Author and Year: Zea mays L., Phytophthora infestans (Mont.) de Bary

Citing the author of the name and the year of publication is an important element of precise reference to a taxon. The rules differ for different groups of organisms, but the general principle is the same: the author and year are indicated after the name, without a comma (in plants) or with a comma (in animals and bacteria).

Plants (ICN):

The author is indicated after the binomen. If the species name was transferred to another genus, the author of the original name (basionym) is indicated in parentheses, and after the parentheses — the author of the new combination. For example:

• Zea mays L. — maize, described by Linnaeus.
• Phytophthora infestans (Mont.) de Bary — late blight, originally described by Montagne as Montagnea infestans, and then transferred by de Bary to the genus Phytophthora. The parentheses here are obligatory (Turland et al., 2025).
• Puccinia graminis Pers. — stem rust, described by Persoon.

The year of publication may be indicated, but is not obligatory. Standard author abbreviations (for example, L. for Linnaeus, Pers. for Persoon) are recommended for use. The list of standard author abbreviations for plants is maintained by the International Plant Names Index (IPNI) (Turland et al., 2025).

Animals (ICZN):

In zoology, the author and year are indicated after the name, often separated by a comma. Parentheses also mean that the species was originally described in another genus. For example:

• Leptinotarsa decemlineata (Say, 1824) — Colorado potato beetle. The parentheses mean that Say originally described it in another genus (ICZN, 1999).
• Apis mellifera Linnaeus, 1758 — honey bee.
• Pieris brassicae (Linnaeus, 1758) — cabbage white butterfly.

Unlike botany, in zoology the year of publication is indicated more often and is considered almost obligatory. Author abbreviations are also standardized, but not as strictly as in botany (ICZN, 1999).

Bacteria (ICNP):

In bacteria, the author and year are indicated after the name. If the name was revised, a construction with two authors is used. For example:

• Erwinia amylovora (Burrill, 1882) Winslow et al., 1920 — causative agent of fire blight of fruit crops. Burrill originally described this species in 1882, and Winslow and colleagues in 1920 transferred it to the genus Erwinia (Parker et al., 2019).
• Pseudomonas syringae van Hall 1902 — causative agent of bacterial spotting.

In bacteriology it is customary to indicate the year of publication, as well as to use standard abbreviations for authors. Lists of approved names are published in the International Journal of Systematic and Evolutionary Microbiology (IJSEM) (Parker et al., 2019).

Viruses (ICTV):

For viruses, the rules of author citation differ. ICTV does not require indicating the author and year after the name of a virus in ordinary scientific texts. Virus names are written in italics with a capital letter, but without author citation. For example:

• Tomato mosaic virus
• Potato leafroll virus
• Tobacco mosaic virus

Official names of virus taxa are approved by ICTV and published in reports. Authorship in the sense of “who described it” is not used for viruses in the way it is in botany or zoology (King et al., 2012).

Virus Names: ICTV Rules, Italics, Word Order

Virus names are subject to special rules that are important to know, since viral plant diseases are widespread in the agricultural sphere.

1. Italics and capital letter. Names of all recognized virus taxa (orders, families, genera, species) are written in italics with a capital letter. For example: Virgaviridae (family), Tobamovirus (genus), Tomato mosaic virus (species). Note: in the species name of a virus, only the first word has a capital letter; the remaining words are lowercase, unless they are proper names (King et al., 2012).

2. Word order. Unlike the binomens of plants and animals, virus names are not binomens in the strict sense. They often consist of several words describing the host, symptom, or place of isolation. For example: Tomato mosaic virus, Potato virus Y, Cucumber mosaic virus. The word order usually follows the English name of the disease or host. Species names of viruses are approved by ICTV and do not obey the principle of priority in the same sense as names of plants or animals (King et al., 2012).

3. Abbreviations. For convenience, standard abbreviations may be used in the text: Tomato mosaic virus (ToMV), Potato virus Y (PVY), Cucumber mosaic virus (CMV). However, at first mention it is necessary to give the full name and the expansion of the abbreviation. Abbreviations are not official taxon names, but merely a working tool (King et al., 2012).

4. Names of orders and families. Orders of viruses have the ending -virales, families — -viridae, subfamilies — -virinae, genera — -virus. For example: Martellivirales (order), Virgaviridae (family), Tobamovirus (genus). These endings are standardized and help determine the rank of a taxon (King et al., 2012).

Bacterial Names: ICNP Rules, Italics, Author

Bacteria are prokaryotes, and their nomenclature is regulated by a separate code, ICNP. For an agronomist it is important to know the basic rules for formatting the names of phytopathogenic bacteria.

1. Italics and capital letter. Names of genera and species of bacteria are written in italics. The generic name is capitalized, the specific epithet is lowercase. For example: Erwinia amylovora, Pseudomonas syringae, Agrobacterium tumefaciens (Parker et al., 2019).

2. Author and year. After the name, the author and year of publication are indicated. If the name was revised, a construction with two authors in parentheses and outside parentheses is used. For example: Erwinia amylovora (Burrill, 1882) Winslow et al., 1920. In bacteriology it is customary to abbreviate “et al.” after three or more authors (Parker et al., 2019).

3. Standard names. ICNP maintains a list of approved names, which is published in IJSEM. These names are official and must be used in scientific literature. If you work with bacterial pathogens, it is recommended to consult this list in order to use current names (Parker et al., 2019).

4. Features. Names of bacteria, like names of plants, may change as a result of taxonomic revisions. For example, the causative agent of bacterial wilt of tomato Ralstonia solanacearum was previously called Pseudomonas solanacearum. When working with old literature, it is necessary to take these changes into account (Sigee, 1993; Sokirko & Gorkovenko, 2019).

Names of Cultivated Plants: ICNCP, Cultivar, Group, Grex

For cultivated plants, which are the main object of the agricultural sphere, there are special rules established by ICNCP. These rules differ from those of ICN and require separate attention.

1. Cultivar. The name of a cultivar consists of the name of the genus or species (in italics) and the cultivar epithet, which is enclosed in single quotation marks and is not italicized. For example:

• Malus domestica 'Antonovka'
• Solanum tuberosum 'Udacha'
• Triticum aestivum 'Mironovskaya 808'

The cultivar epithet is written with a capital letter if it is a proper name or code, but may also be lowercase if it is an ordinary word. The main thing is that it is always in quotation marks (Brickell et al., 2016).

2. Abbreviation cv. Since 1996, the abbreviation cv. (cultivar) before a cultivar epithet is not used. Incorrect: Triticum aestivum cv. Mironovskaya 808. Correct: Triticum aestivum 'Mironovskaya 808' (Brickell et al., 2016).

3. Group. The name of a Group consists of the name of the genus or species (in italics) and the Group epithet, which includes the word Group (or its equivalent in other languages). The word Group is written with a capital letter. For example:

• Brassica oleracea Gemmifera Group (Brussels sprouts)
• Rosa Polyantha Group (polyantha roses)

The Group epithet is not enclosed in quotation marks (Brickell et al., 2016).

4. Grex. This category is used only in orchid nomenclature. The name of a grex consists of the genus name and the grex epithet, followed by the word grex or the abbreviation gx. For example: Paphiopedilum Sorel grex. The grex epithet is not enclosed in quotation marks (Brickell et al., 2016).

5. What is not a taxonomic rank. It is important to understand that cultivar, Group, and grex are not taxonomic ranks in the sense of ICN. They are special categories for classifying plants that arose in cultivation. They are not integrated into the hierarchy species → genus → family. For example, the cultivar Malus domestica 'Antonovka' belongs to the species Malus domestica, but the cultivar itself is not an infraspecific taxon in the botanical sense (Brickell et al., 2016).

Typical Errors in Scientific Works and Reports

Even experienced specialists sometimes make errors in formatting names. Here are the most common ones.

1. Incorrect use of italics. Only generic and specific names (as well as infraspecific epithets) should be italicized. Names of families, orders, classes, and divisions are written in roman type. For example, correct: Triticum aestivum (italics), but Poaceae (roman). Error: Poaceae (italics) — incorrect.

2. Capital letter in the specific epithet. The specific epithet is always written with a lowercase letter, even if it is formed from a proper name. Error: Triticum Aestivum. Correct: Triticum aestivum.

3. Absence of parentheses when the genus changes. If a species was transferred to another genus, the author of the original name is indicated in parentheses. Error: Phytophthora infestans Mont. de Bary. Correct: Phytophthora infestans (Mont.) de Bary.

4. Use of cv. The abbreviation cv. is outdated. Error: Solanum tuberosum cv. Udacha. Correct: Solanum tuberosum 'Udacha'.

5. Incorrect abbreviation of the genus. The abbreviation of a genus must be unambiguous. If the text contains several genera beginning with the same letter, the abbreviation may confuse. Error: T. aestivum and T. pratense (if referring to Triticum and Trifolium). Better: Triticum aestivum and Trifolium pratense.

6. Confusion with synonyms. When citing a taxon, it is important to use the current name, not an outdated synonym. For example, Puccinia graminis f. sp. tritici is a special form, not a separate species. If you use a synonym, it should be indicated as a synonym, not as the main name (Turland et al., 2025).

7. Incorrect citation of viruses. Virus names are written in italics with a capital letter, but without author citation. Error: Tomato mosaic virus (ToMV) Smith, 1935. Correct: Tomato mosaic virus (ToMV). The author and year for viruses are not indicated in ordinary text (King et al., 2012).

8. Use of outdated names. Taxonomic revisions lead to changes in names. For example, the family Liliaceae in the broad sense is no longer recognized; many genera have been transferred to other families. If you use an outdated name, this may be perceived as an error. It is recommended to consult modern databases (APG IV, 2016; Watson, 2015).

9. Incorrect formatting of bacterial authors. In bacteria, the author and year are indicated after the name, often with “et al.” for three or more authors. Error: Erwinia amylovora Burrill. Correct: Erwinia amylovora (Burrill, 1882) Winslow et al., 1920.

10. Mixing codes. Names of plants, animals, bacteria, and viruses are regulated by different codes. One cannot apply ICN rules to animal names or ICZN to plant names. Error: using parentheses in author citation of a plant according to ICZN rules. Correct: for plants — Zea mays L., for animals — Apis mellifera Linnaeus, 1758.

Practical Recommendations

To avoid errors and improve the quality of your work, follow these recommendations.

1. Use modern databases. For plants — International Plant Names Index (IPNI), Tropicos, The Plant List; for fungi — Index Fungorum, MycoBank; for bacteria — LPSN (List of Prokaryotic names with Standing in Nomenclature); for viruses — ICTV online. These databases contain current names and author citation (Watson, 2015).

2. Check names in several sources. If there are doubts, consult several databases. Remember that databases may update with a delay, so it is better to use several sources (Watson, 2015).

3. Follow taxonomic revisions. If you work with a group for which molecular phylogenetic works have recently been published, check whether the names have changed. For example, for angiosperms — APG IV (2016), for fungi — regular reviews in journals (Sokirko & Gorkovenko, 2019).

4. Use unique identifiers. For unambiguous identification of taxa, use LSID, GUID, or other unique identifiers if the database provides them. This is especially important when working with large data sets (Watson, 2015).

5. Be consistent. Within one work, use the same taxonomic system and the same names. If you cite synonyms, clearly indicate which name you consider the main one.

6. Educate colleagues and students. Correct citation of names is part of professional culture. Share knowledge with colleagues and students, and draw attention to errors in collective works.

Section Conclusion

The practice of citing taxon names is not a trifle but an important aspect of scientific and practical work. Correct formatting of names ensures precision of communication, respect for authors, and stability of knowledge. Errors in names can lead to incorrect identification of organisms, which in the agricultural sphere is fraught with incorrect decisions on plant protection, breeding, and production.

In the next, final section, we will summarize the lecture and discuss why nomenclature ensures stability and continuity of knowledge, and why taxonomic hierarchy is a tool, not a dogma.

Nomenclature Ensures Stability and Continuity of Knowledge

Throughout the lecture, we repeatedly returned to one key idea: nomenclature is the foundation of biological communication. Without it, science could not accumulate and transmit knowledge. Every scientific name is not merely a label but the result of a long history of research, taxonomic revisions, and international agreements (Turland et al., 2025; Judd et al., 2018).

The international codes of nomenclature — ICN, ICZN, ICTV, ICNP, and ICNCP — are sets of rules that ensure the stability of names. The principles of priority, typification, and independence of codes allow avoiding chaos and confusion. Thanks to these principles, a name once given to a taxon is preserved forever, even if our ideas about its relationships change (Turland et al., 2025; ICZN, 1999; Parker et al., 2019; King et al., 2012; Brickell et al., 2016).

Nomenclature is not a frozen system. It develops together with science. Taxonomic revisions based on molecular phylogenetic data lead to a revision of taxon boundaries and, as a consequence, to changes in names. But these changes are not chaotic — they obey strict rules and are aimed at creating a more natural, monophyletic classification (APG IV, 2016; Webster & Weber, 2007; Sokirko & Gorkovenko, 2019).

Taxonomic Hierarchy Is a Tool, Not a Dogma

We have examined in detail taxonomic hierarchy — a system of ranks from species to domain. This hierarchy allows us to order the entire diversity of living organisms and see their relationships. However, it is important to remember that hierarchy is a tool, not a dogma. Ranks (species, genus, family, order, etc.) are human constructs, conventional “shelves” onto which we place taxa for convenience (Stuessy, 2009; Judd et al., 2018).

We discussed the fundamental distinction between clade and taxonomic rank. A clade is an objective reality, a branch of the evolutionary tree. A rank is a subjective label that we attach to a clade. Modern systematics strives for all recognized taxa to be monophyletic, but historically established ranks do not always correspond to this. That is precisely why systematics is in a state of constant revision: as data accumulate, we refine the boundaries of clades and revise ranks (Judd et al., 2018; Simpson, 2015; APG IV, 2016).

We saw that different databases (NCBI, GBIF, Tropicos, Index Fungorum) may use different names and ranks for the same taxa. This is not an error but a consequence of different taxonomic concepts, data sources, and update delays. For a specialist in the agricultural sphere this means the need to critically evaluate information and use unique identifiers for unambiguous identification of taxa (Watson, 2015).

Correct Citation of Names Is an Indicator of the Professional Culture of an Agronomist

We examined in detail the practical rules for citing taxon names. Italics for generic and specific names, a capital letter only for the genus, correct use of authors and parentheses, features of citing viruses, bacteria, and cultivated plants — all these are not trifles but important elements of professional work (Turland et al., 2025; ICZN, 1999; Parker et al., 2019; King et al., 2012; Brickell et al., 2016).

Errors in names can lead to incorrect identification of organisms, which in the agricultural sphere is fraught with incorrect decisions on plant protection, breeding, and production. For example, if you incorrectly identify a disease agent, you may apply an ineffective control method or cause harm to the environment. If you use an outdated name, your data may be incorrectly interpreted by colleagues (Watson, 2015; Sigee, 1993).

Correct citation of names is an indicator of professional culture. It demonstrates respect for authors, precision, and attention to detail. In scientific publications, reports, recommendations, and even in everyday work, an agronomist must use current scientific names and format them correctly (Judd et al., 2018; Stuessy, 2009).

What We Learned and What It Means for Practice

Let us briefly summarize the key conclusions of our lecture and think about how they can be applied in practical work.

1. Nomenclature is the basis of communication. Without a unified system of names, scientific knowledge could not accumulate and be transmitted. Use scientific names in your work, not only vernacular or commercial ones.

2. Several international codes exist. ICN for plants, fungi, and algae; ICZN for animals; ICTV for viruses; ICNP for prokaryotes; ICNCP for cultivated plants. Know which code applies to your group of organisms.

3. Binary nomenclature is a universal language. Genus + specific epithet. The generic name is capitalized, the specific epithet is lowercase. Everything is in italics.

4. Author and year are an important part of the name. They help accurately identify a taxon and trace its history. Use correct parentheses and abbreviations.

5. Typification is the basis of stability. Each name is tied to a specific type specimen. Understanding types (holotype, lectotype, neotype, epitype) helps to make sense of taxonomic revisions.

6. Taxonomic hierarchy is a tool. Ranks are conventional steps. Do not confuse them with clades. Modern systematics strives for monophyly, but traditional ranks do not always correspond to it.

7. Clade ≠ rank. A clade is an evolutionary branch, an objective reality. A rank is a formal step, a human construct. The same clade may have different ranks in different systems.

8. Different databases use different names. This is not an error but a consequence of different concepts and update delays. Check information in several sources and use unique identifiers.

9. Citation rules differ for different groups. Italics, capital letters, author citation, parentheses — all these have their own features for plants, animals, bacteria, viruses, and cultivated plants.

10. Correct citation is professional culture. It ensures precision, respect for authors, and stability of knowledge. Follow the relevance of names and do not allow errors.

Closing Word

In conclusion, it is worth emphasizing that systematics and nomenclature are not merely “the science of names.” They are a tool for understanding biological diversity, which allows us to understand the relationships of organisms, predict their properties, and effectively manage agroecosystems. For an agronomist, knowledge of nomenclature and taxonomic hierarchy is not an academic luxury but a professional necessity.

We live in an era of rapid data accumulation. Molecular phylogenetic studies are revolutionizing our ideas about the relationships of organisms. Taxonomic revisions occur constantly, and names change. This may seem inconvenient, but it is a sign that science is developing. Our task is to keep abreast of these changes and use current knowledge in our work (APG IV, 2016; Watson, 2015).

Remember: nomenclature ensures stability, but not rigidity. It allows us to preserve the continuity of knowledge, even when our ideas about classification change. Taxonomic hierarchy is a tool, not a dogma. It helps us order diversity, but must not become an obstacle to new discoveries.

Correct citation of taxon names is an indicator of the professional culture of an agronomist. It demonstrates your respect for science, for colleagues, and for those who will use your results. Be attentive to details, follow current names, and do not be afraid to ask questions if something raises doubts.

We hope that this lecture has helped you systematize knowledge about nomenclature and taxonomic hierarchy and that you will be able to apply it in your professional activity. In the following lectures, we will continue studying the systematics and taxonomy of organisms of the agricultural sphere, going deeper into specific groups and methods of their classification.