A botanical name is a formal scientific name conforming to the International Code of Nomenclature for algae, fungi, and plants (ICN) and, if it concerns a plant cultigen, the additional cultivar or Group epithets must conform to the International Code of Nomenclature for Cultivated Plants (ICNCP). The code of nomenclature covers "all organisms traditionally treated as algae, fungi, or plants, whether fossil or non-fossil, including blue-green algae (Cyanobacteria), chytrids, oomycetes, slime moulds and photosynthetic protists with their taxonomically related non-photosynthetic groups (but excluding Microsporidia)."
The purpose of a formal name is to have a single name that is accepted and used worldwide for a particular plant or plant group. For example, the botanical name Bellis perennis denotes a plant species which is native to most of the countries of Europe and the Middle East, where it has accumulated various names in many languages. Later, the plant was introduced worldwide, bringing it into contact with more languages. English names for this plant species include: daisy, English daisy, and lawn daisy. The cultivar Bellis perennis 'Aucubifolia' is a golden-variegated horticultural selection of this species.
Type specimens and circumscription
The botanical name itself is fixed by a type, which is a particular specimen (or in some cases a group of specimens) of an organism to which the scientific name is formally attached. In other words, a type is an example that serves to anchor or centralize the defining features of that particular taxon.
The usefulness of botanical names is limited by the fact that taxonomic groups are not fixed in size; a taxon may have a varying circumscription, depending on the taxonomic system, thus, the group that a particular botanical name refers to can be quite small according to some people and quite big according to others. For example, the traditional view of the family Malvaceae has been expanded in some modern approaches to include what were formerly considered to be several closely related families. Some botanical names refer to groups that are very stable (for example Equisetaceae, Magnoliaceae) while for other names a careful check is needed to see which circumscription is being used (for example Fabaceae, Amygdaloideae, Taraxacum officinale).
Forms of plant names
Depending on rank, botanical names may be in one part (genus and above), two parts (various situations below the rank of genus) or three parts (below the rank of species). The names of cultivated plants are not necessarily similar to the botanical names, since they may instead involve "unambiguous common names" of species or genera. Cultivated plant names may also have an extra component, bringing a maximum of four parts:
in one part
Plantae (the plants) Marchantiophyta (the liverworts) Magnoliopsida (class including the family Magnoliaceae) Liliidae (subclass including the family Liliaceae) Pinophyta (the conifers) Fagaceae (the beech family) Betula (the birch genus)
in two parts
Acacia subg. Phyllodineae (the wattles) lchemilla subsect. Heliodrosium Berberis thunbergii (Japanese barberry) a species name, i.e., a combination consisting of a genus name and one epithet Syringa 'Charisma' – a cultivar within a genus Hydrangea Lacecap Group – a genus name and Group epithet Lilium Darkest Red Group – a genus name and Group epithet Paphiopedilum Greenteaicecreamandraspberries grex snowdrop 'John Gray' – an unambiguous common name for the genus Galanthus and a cultivar epithet
in three parts
Calystegia sepium subsp. americana (American hedge bindweed), a combination consisting of a genus name and two epithets Crataegus azarolus var. pontica (a Mediterranean hawthorn) Bellis perennis 'Aucubifolia' – a cultivar Brassica oleracea Gemmifera Group – a species name and Group epithet
in four parts
Scilla hispanica var. campanulata 'Rose Queen' – a cultivar within a botanical variety apart from cultivars, the name of a plant can never have more than three parts.
Components of plant names
A botanical name in three parts, i.e., an infraspecific name (a name for a taxon below the rank of species) needs a "connecting term" to indicate rank. In the Calystegia example above, this is "subsp.", for subspecies. In botany there are many ranks below that of species (in zoology there is only one such rank, subspecies, so that this "connecting term" is not used in zoology). A name of a "subdivision of a genus" also needs a connecting term (in the Acacia example above, this is "subg.", subgenus). The connecting term is not part of the name itself.