Reading plant scientific names: genus, epithet, f. and 'Compacta'

Under the title of each plant page there is a scientific name such as Hoya carnosa (L.f.) R.Br. This article uses plants already on the site to explain what each part of a scientific name means.

The rules come mainly from two international codes: the International Code of Nomenclature for algae, fungi, and plants (the Madrid Code, published in 2025), which governs plant names in general, and the International Code of Nomenclature for Cultivated Plants (ninth edition, 2016), which governs cultivar names.

Why scientific names matter

A plant often has more than one Chinese name. The Flora of China gives 五唇蘭 as the Chinese name of the orchid this site calls 朵麗蘭, and the Taiwan Biodiversity Network lists 仙人蕈 for the cactus this site calls 烏羽玉. Going by common names alone, you could easily take them for different plants.

Scientific names follow clear rules. One principle of the Code is that a taxonomic group with a particular circumscription, position and rank can have only one correct name. Another is that scientific names are treated as Latin, whatever their origin.

The basic structure: genus plus epithet

The name of a species is a two-part combination: the genus name followed by a specific epithet. In Hoya carnosa, Hoya is the genus and carnosa is the specific epithet.

The genus name is written with an initial capital letter, and the Code recommends that specific and infraspecific epithets begin with a lower-case letter.

As for italics, the Code itself prints scientific names in italic, but states that it sets no binding standard, because typography is a matter of editorial style; in the interest of international uniformity, it suggests following its practice. This site italicises scientific names too.

The principal ranks, from largest to smallest, are kingdom, division or phylum, class, order, family, genus and species, so every species belongs to a genus. The plant index on this site is grouped by genus.

The names and brackets after a scientific name

A scientific name is often followed by abbreviated names, such as (L.f.) R.Br. after Hoya carnosa. These are the authors of the name. Citing them is optional; the Code says that in publications, particularly those dealing with taxonomy and nomenclature, citing the authors may be desirable.

The brackets have a specific meaning. When a name is based on an earlier published name, for example when a species is moved to another genus, the author of the earlier name goes in brackets, followed by the author of the new name.

Three plants on this site are examples, and POWO lists the earlier names as their homotypic synonyms:

• Hoya carnosa (L.f.) R.Br.: originally Asclepias carnosa, published by L.f.
• Phalaenopsis pulcherrima (Lindl.) J.J.Sm.: originally Doritis pulcherrima, published by Lindl.
• Dioscorea elephantipes (L'Hér.) Engl.: originally Tamus elephantipes, published by L'Hér.

Synonyms: why 朵麗蘭 became a Phalaenopsis

A taxon can have several names, and POWO lists the ones it does not use as synonyms of the species. Names based on the same type are called homotypic synonyms.

This site's 朵麗蘭 is a good example. POWO now lists the genus Doritis as a synonym of Phalaenopsis, so Doritis pulcherrima has become Phalaenopsis pulcherrima. The Flora of China, however, still treats the species as Doritis pulcherrima.

That does not mean one of them is wrong. The Code says there is one correct name "with a particular circumscription, position, and rank"; different views on classification, such as whether Doritis should be merged into Phalaenopsis, lead to different correct names.

The curled-leaf hoya runs into something similar: POWO lists the name Hoya compacta as a synonym of Hoya carnosa.

Ranks below species: subsp., var., f.

Below species, the Code provides ranks including subspecies, variety (varietas) and form (forma). The name of an infraspecific taxon adds a connecting term for the rank, such as subsp., var. or f., followed by an epithet. The Taiwan Biodiversity Network likewise divides ranks below species into subspecies, variety, form and cultivar.

This site's example is Phalaenopsis pulcherrima f. alba (O.Gruss & Roeth) Christenson, where f. means form. It was published in 2001 in Phalaenopsis: a monograph.

This one name ties several ideas together: O.Gruss & Roeth in brackets are the authors of the earlier name, and POWO lists the name as a synonym of Phalaenopsis pulcherrima var. pulcherrima. In other words, in the classification POWO follows, the white form is not kept as a separate form but placed under the typical variety. A name existing and a name being the accepted correct name are two different things.

Cultivars: why 'Compacta' is in single quotes

Cultivars are not governed by the first Code but by the International Code of Nomenclature for Cultivated Plants.

Under that Code, a cultivar is an assemblage of plants selected for a particular character or combination of characters, which remains distinct, uniform and stable in those characters when propagated by appropriate means. The Code also notes that the Chinese word 品種 is a common equivalent of "cultivar".

Cultivar names follow a few rules:

• The cultivar epithet goes in single quotation marks, as in Hoya carnosa 'Compacta'.
• Double quotation marks, cv. and var. are not to be used to mark a cultivar. Before 1996, cv. was allowed, so you may still see it on older labels in botanic gardens.
• Each word of a cultivar epithet starts with a capital letter.
• If scientific names are in italics, the cultivar epithet should not be, so that the two stand apart.

The Code also states that variety (var.) and form (f.) are not equivalent to cultivar. So although f. alba and 'Compacta' both follow a scientific name, they mean different things: f. is a botanical rank, while the name in single quotes is a cultivar.

Hindu rope, described by Iowa State University Extension, is the cultivar 'Compacta' of Hoya carnosa, with tightly curled leaves.

About the plant index on this site

• Below each plant page title is the full scientific name with its authors, taken from databases such as POWO.
• The plant index is grouped by genus, and the genus is taken only from a verified scientific name.
• For plants whose scientific name has not been verified yet, this site does not guess the genus from the Chinese name.