Botanical Nomenclature for Hybrids: Rules and Naming Conventions
In the world of plant science, identifying a plant's origin is crucial for accurate classification. When a plant is the result of a cross between two different species or genera, it is known as a hybrid. While not every hybrid requires a unique name, the International Code of Nomenclature for algae, fungi, and plants (ICNafp) provides a rigorous framework for how these plants should be named and documented to ensure global scientific consistency.
Key Facts
- Hybrids can be identified by a formal hybrid name, a formula listing parents, or a combination of both.
- The multiplication sign (×) is the standard symbol used to denote a hybrid.
- Nothotaxa is the general term for hybrid taxa, combining "notho-" (hybrid) and "taxon".
- Intergeneric hybrids (crosses between different genera) often use condensed formulas.
- Orchid hybrids use a specialized naming system known as Grex names.
Methods of Identifying Hybrids
According to the ICNafp, authors have several options when dealing with a hybrid. While a formal name can be created if deemed necessary—typically for naturally occurring hybrids—it is often recommended to use the names of the parent plants, as this provides more biological information.
Hybrid Formulas
A hybrid may be indicated by a formula that lists the parents linked by the multiplication sign (×). To maintain consistency, these names or epithets are usually listed in alphabetical order. If a specific direction of the cross is important, scientists use sexual symbols (♀ for female and ♂ for male) or place the female parent first in the sequence.
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Grex Names
Specific to orchids, Grex names are used to identify hybrids. Unlike standard hybrid names, a Grex name does not cover F2 hybrids (crosses between plants within the same grex) or back-crosses (crosses between a grex member and one of its parents).
Understanding Nothotaxa and Ranks
Hybrids are classified as nothotaxa. When parents of different taxonomic ranks are involved, the resulting nothotaxon is assigned the lowest rank of the parents. The naming convention changes based on the relationship between the parents:
- Nothospecies: If the parents are within the same genus, the hybrid is a nothospecies (e.g., Pyrus × bretschneideri).
- Nothogenus: If the parents belong to different genera, a nothogenus name is used (e.g., × Pyraria irregularis, a hybrid of Aria edulis and Pyrus communis).
Historically, the term nothomorph was used for ranks subordinate to a nothospecies, but these are now treated as varieties.
Publication and Formatting Rules
The publication of hybrid names varies by rank. Nothogenera and subdivisions of a genus (such as notho-sections or notho-series) can be published by simply listing the parent taxa; they do not require a formal scientific description or a designated type.
Visual Indicators of Hybrids
There are two primary ways to visually mark a hybrid name:
- The Multiplication Sign (×): Placed before the name of an intergeneric hybrid (e.g., × Sorbaronia) or before the epithet of a species hybrid (e.g., Iris × germanica).
- The Prefix notho-: Attached to the rank, such as Crataegus nothosect. Crataeguineae.
It is important to note that neither the "×" symbol nor the "notho-" prefix is considered part of the actual name for nomenclatural purposes like synonymy. A taxonomist may choose to use Drosera × anglica to highlight its hybrid nature or Drosera anglica to emphasize its status as a species.
Complex Intergeneric Hybrids
For hybrids between two genera, a condensed formula is often used (e.g., × Agropogon for Agrostis and Polypogon). When a hybrid involves four or more genera, the name is typically derived from a person's name with the suffix -ara (e.g., × Belleara). Hybrids of three genera may use either a condensed formula or the -ara suffix.
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Summary of Hybrid Nomenclature
| Type | Scope | Naming Convention | Example |
|---|---|---|---|
| Species Hybrid | Same genus | Genus + × + epithet | Pyrus × bretschneideri |
| Intergeneric Hybrid | Different genera | × + Nothogenus name | × Sorbaronia |
| Orchid Hybrid | Orchidaceae family | Grex name | Grex-specific |
| Complex Hybrid | 4+ genera | Person's name + -ara | × Belleara |
Frequently Asked Questions
What is the difference between a hybrid name and a hybrid formula?
A hybrid name is a formal botanical name given to a hybrid, whereas a hybrid formula is a descriptive listing of the parent plants linked by a multiplication sign (×), which is often considered more informative.
Does a hybrid name only apply to plants that look identical?
No. A hybrid name applies to all progeny of the parents, regardless of morphological variation. For example, Magnolia × soulangeana covers a wide range of flower colors resulting from the cross of Magnolia denudata and Magnolia liliiflora.
What symbol is used to denote a hybrid, and why?
The standard symbol is the multiplication sign (×). While Carl Linnaeus originally used the symbol for Mercury (☿), he later abandoned it in favor of the multiplication sign.
How is the rank of a nothotaxon determined?
If the postulated parents of a hybrid differ in taxonomic rank, the resulting nothotaxon is assigned the lowest rank among the parents.
What is a condensed formula in botanical naming?
A condensed formula is a shortened name created for intergeneric hybrids, such as × Agropogon, which blends the names of the parent genera (in this case, Agrostis and Polypogon).