Although botanical names are often referred to as "Latin" names, in fact, many of them are Greek in origin. The term "Latin name" comes from the fact that all botanical names, originating from Latin, Greek, other languages, place names and people's names, are declined following the rules of Latin grammar. While botanical nomenclature is rather complicated, the way to write these names is fairly straightforward. In this explanation we use the expressions italicized to mean slanting font (or type style) and Roman to mean upright font. (Note that orchids have their own style of nomenclature. You can learn more about understanding orchid names in this Guide to Orchid Names.)

Genus and species:

Names should always be italicized or underlined. The first letter of the genus name is capitalized but the specific epithet is not. Most commonly, italicized font is used when typing the name and underlining is used when handwriting the name.

• Example: Lavandula latifolia or Lavandula latifolia

If the meaning is clear, for instance when you are listing a series of plants all in the same genus, the generic name can be abbreviated.

• Example: Lavandula latifolia, L. stoechas and L. canariensis are three lavender species native to Spain.

If the specific epithet is not known or not needed then it can be indicated by sp. or spp. (plural).

• Example: Rosa sp. 

Authority name:

In botanical journals and texts, the specific epithet may be followed by the name of the person responsible for naming the species. This name should not be italicized. The names of older authorities responsible for naming many species are often abbreviated.

• Example: Arum maculatum L., where L. is an abbreviation for Linnaeus

Sometimes one person has registered the name but credits another botanist or collector for the discovery.

• Example: Euphorbia pulcherrima Willd. ex Klotzsch indicates that Johann Friedrich Klotzsch published this name but credits the German botanist Carl Ludwig Willdenow (Willd.) as the authority who identified the species.

You will also see botanical names where the plant has been reclassified under a new name and both the original naming authority and the authority responsible for the new name are identified.

• Example: Gentiana bicuspidata (G.Don) Briq. was originally named Pneumonanthe bicuspidata by the Scottish botanist George Don in 1837 and later reclassified as Gentiana bicuspidata by John Isaac Briquet in 1931.

Ranks below species (indicating natural variants):

Plants that are very similar but with some horticulturally significant variation from the species type may be recognized as a subspecies (subsp.), variety (var.)  or form (f.) of the species, in declining order of distinctiveness. The botanical variant is italicized, and the abbreviation is not. Both are in lower case font.

• Example: Salvia lavandulifolia subsp. amethystea
• Example: Juniperus pingii var. wilsonii

Synonyms:

Some plants have two accepted names or a name that is closely associated with the plant but no longer accepted. In this case, the less-used or unaccepted name is indicated by the term syn. in Roman font. It is not essential to include both names but is helpful if the synonym adds clarity.

• Example: Senna alata (syn. Cassia alata)

Cultivar names (indicating variants selected or derived by gardeners):

Are not italicized. They can be indicated by cv. or, more commonly, placed in single quotation marks. The cultivar name can follow a genus, a specific epithet, a hybrid or an infraspecific taxon name (such as a subspecies or variety). The first letter(s) in each word in the cultivar name is capitalized.

• Example:  Dianthus deltoides 'Bright Eyes' or Dianthus deltoides cv. Bright Eyes
• Example: Helianthus 'Happy Days'
• Example: Euonymus hamiltonianus subsp. sieboldianus 'Coral Charm'

You may also see shortened versions of cultivar names used, particularly in nursery settings, because they are less cumbersome. Nonetheless, Euonymus 'Coral Charm', for instance, is not a correct botanical name for the above plant following the conventions of the International Code of Nomenclature for Cultivated Plants.

Hybrids (either natural or derived by gardeners):

Can be indicated by an × (multiplication sign). Both the genus name and the specific epithet are italicized.

• Example: Platanus occidentalis × Platanus orientalis (which can also be expressed as Platanus occidentalis × P. orientalis). Sometimes the hybrid is given a new name of its own: Platanus × hispanica, in this case. The × in the new name indicates that it is a hybrid.

Grex names:

Are largely confined to orchids (the term refers to seedling derived from a hybrid cross). The grex name is written in Roman font, e.g. Pleione Fujiama 'Teal', where Fujiama is the grex name. Learn more about grex names in Understanding Orchid Names.

Trade names:

Some cultivars have trade names or trademarks. This name is not the officially registered name for the plant, but a marketing name assigned by the seller. These should be styled in a different font, for example in all capital letters and with a  ® for registered trademark or ™ if they are trademarked.

• Example: Clematis SHIMMER 'Evipo098' where SHIMMER is the trade name and 'Evipo098' is the registered cultivar name. This is a common situation for rose cultivars and you can read more about proper styling of their names in our article  What is the proper way to write a botanical name for a rose cultivar?

Family names:

There is some confusion about how family names should be written. In American usage the family name is not usually italicized.

• Example: Pinaceae

However the most recent edition of the International Code of Nomenclature for algae, fungi, and plants (which is the official authority on plant names) recommends that all plant names be in a different font from the rest of the text. The Royal Horticultural Society (U.K.) recommends that family names be italicized. Plant labels in botanical gardens usually have the family name in capital letters,  for instance PINACEAE.

Common names:

There are no rules governing common names but it is standard usage to write the names in lower case (except for proper nouns) and to use Roman font.

• Example: Vinca minor is known by the common name periwinkle and Viola tricolor is often called Johnny jump up.

When the name of the genus is also used as a common name, it is expressed all in lower case and without italics for that purpose only.

• Example: I want to add a lily and a blue salvia to this planter and Salvia guarantica 'Blue Enigma' might be a good choice.

Related Guides from NYBG:

Understanding Plant Labels at the New York Botanical Garden

Understanding Orchid Names

What is the proper way to write a botanical name for a rose cultivar?

Other Resources:

The International Code of Nomenclature

RHS recommended style

International Code of Nomenclature for Cultivated Plants

- Courtesy of NYBG Plant Information Service