Cultivars and Ranks of Taxa According to the ICBN and ICNCP
Jesse L. Saylor, August 12, 2009
These are the subcategories or units of classicification according to the ICBN (International Code
of Botanical Nomenclature, Tokyo Code, ed. by Greuter, 1994), with additions from the ICNCP (International
Code of Nomenclature for Cultivated Plants, Cultivated Plant Code, ed. by Trehane, 1995).
Endings are listed after each category if specified in the ICBN. More commonly used categories are in
Red (shaded in black and white printing).
Division or Phylum (-phyta)
Subdivision or Subphylum (-phytina) [Walters and Keil use -icae, following
Cronquist, Takhtajan and Zimmerman(1966)]
Class (-opsida) [KUB uses -atae]
Superorder (-anae; iflorae in past; put in Tokyo code 1994)
Family (-aceae, with 8 exceptions listed below)
Genus (plural is genera)
species (abbr. sp. for singular; spp. for plural)
subspecies (abbr. subsp.)
variety (abbr. var.)
`Cultivar’ or cv. Cultivar
forma (abbr. f.)
The Cultivar is from the ICNCP (Cultivated Plant Code) and all the other categories are listed in
the ICBN (Tokyo Code). No individual plant has all the categories listed above.
The word taxa (singular: taxon) refers to names of taxonomic groups of any rank.
Botanical nomenclature is independent of zoological and bacteriological nomenclature.
The principle of priority of publication means that the earliest published name is the most correct.
The starting point for vascular plant (Spermatophyta or seed plant, and Pteridophyta or Fern) names is Linnaeus
and his Species Plantarum, edition 1, May 1, 1753.
With the family names ending in -aceae, there are 8 exceptions or names of long usage that are
listed as valid; thus either name can be used. They are: Compositae or Asteraceae, Cruciferae or Brassicaceae,
Gramineae or Poaceae, Guttiferae or Clusiaceae, Labiatae or Lamiaceae, Leguminosae or Fabaceae,
Palmae or Arecaceae, Umbelliferae or Apiaceae. I often use the exceptions, but will note the -aceae names.
Scientific names (also called Latin names or botanical names) are binomial and are composed
of the Genus and the species (or specific epithet) with the Genus standing by itself (like peoples last names)
and the species being used again and again with different genera (like peoples first names).
A genus name is only used once for plants and not repeated for other plants. The Genus name has meaning by
itself (Ex. Acer means Maple). Genus name are always capitalized.
A species name cannot stand by itself, since the same species name is used with many genera (Ex. Cornus alba,
Ipomoea alba, Quercus alba, Populus alba, Salix alba, etc.). Genus and species names are Latin names and all
Latin names are italicized or underlined. Cultivar names are not underlined or italicized.
In taxonomic and botanical literature (including Hortus III, and RHS), the Genus and species is followed
by the abbreviation of the author who named and described the plant [Ex. Acer rubrum L.]. If the name was
revised or changed, the previous author is in parentheses [Actinidia arguta (Sieb. and Zucc.)Miq.]. The author
name is important, especially when two people use the same name in describing two different plants; the author
name is the only way to know which plant species is being referenced. This has happened in the past when two
people in different countries described two different plants and used the same Latin name. Remember, the author
is not necessarily an authority on the plant or plants that he or she names.
A botanical variety is found in the wild and described as such. A cultivar is found in cultivation.
Sometimes a cultivar is called a variety or form but these are not the proper terms. Cultivated varieties
or cultivars are not botanical varieties. However, the ranks can be similar, such as a white flowered selection of
a blue flowered plant; which would be var. alba if first found in the wild, or cv. Alba if first found in cultivtion.
Cultivar names are always capitalized, and are either written with single quotes around them
(Ex. Acer rubrum `Red Sunset’) or as cv. before the name (Ex. Acer rubrum cv. Red Sunset). Cultivar names can
be more than one word, but other names can only be one word. Cultivar names are not italicized or underlined.
The term cultivar is derived from the words cultivated variety. In the ICNCP(Brickell 1995) “A cultivar
is a taxon that has been selected for a particular attribute or combination of attributes, and that is clearly
distinct, uniform, and stable in its characteristics and that, when propagated by appropriate means, retains
those characteristics.” The previous cultivated codes (Brickell 1980 and earlier) used this definition: “The
international term cultivar denotes an assemblage of cultivated plants which is clearly distinguished by any
characters (morphological, physiological, cytological, chemical, or others), and which, when reproduced
(sexually or asexually), retains its distinguishing characters.” The ICNCP also states: “The words “variety”
and “form” (or their equivalent in other languages) must not be used as synonyms for the word cultivar when
fulfilling the Articles of this Code, nor in translations of this Code.” This also applies to the use of the term
“strain”, since it has been widely used with different meanings.
Clones (which are asexually propagated from any part of a plant), may be given cultivar names. Clones
derived from aberrant (abnormal) growth may be given cultivar names. Graft-chimaeras (composed of tissues
from two different plants and originated by grafting) may be given cultivar names (Ex. Syringa `Correlata’, which
combines tissues from Syringa x chinensis and Syring vulgaris). F1 hyrids (the result of a repeatable single cross
between two pure-bred lines), cultivar groups [Ex. Tulipa Darwin Group; Solanum tuberosum ‘Desiree’
(Red-skinned Group); the group name is in parentheses if a specific cultivar is listed], and a number of other
categories are specifically listed as items that can be given cultivar names.
The term Grex (a hybrid group of known parentage) is mentioned, but the code specifically indicates that
it should not be used for any plants except orchids, where it has been in use for some time. However, Grex is
now used by some authors for more than just orchids.
Hybrids are discussed in the ICBN, and are indicated by the multiplication sign x, or by the addition of the
prefix notho- to the term denoting the rank of the taxon. Intergeneric hybrids (between two different genera) have
the x before the name (Ex. X Mahoberberis). Interspecific hybrids (between two or more species) have the
x before the epithet of species name (Ex. Mentha x piperita). Also note that the x is not underlined or italicized
like the Latin names.
The ICBN includes lists of family names and genus names that are conserved over the oldest or most valid
name. These lists are established to provide some stability in names of long usage, and to eliminate specific