Essential Oils: Botanical Classification
Copyright © Tony Burfield 2000-2005.

Pre-amble.
A lack of the concise and unambiguous botanical naming of plant sources that provide useful products, is unfortunately quite evident across the board in modern literature, whether trade sources, professional published papers, or official documents are considered. This document is an extremely brief look at a more correct approach.

Modern Botanical Nomenclature.
A system to distinguish plants which is based purely on common names would be both ambiguous and confusing, and could group together plants which bear similar names, but are not related to each other e.g. here are some listings for Laurel (Mabberley 1998):

Alexandrian Laurel Calophyllum inophyllum L.
Bay Laurel Laurus nobilis L.
Californian Bay Laurel Umbellularia californica (Hook. & Arn.) Nutt.
Cherry Laurel Prunus laurocerasus L.
Chinese Laurel Antidesma bunius (L.) Sprengel etc. etc.

So, today, plants are classified under the binomial system invented by Carl Linneus (1707-78), a Swedish botanist. In this system, the first name given is that of the genus, and the second, that of the specific epithet e.g. for creeping or Corsican mint Mentha requienii Bentham, the genus is Mentha, of the Labiatae family, M. requienii being one of some 25 species of aromatic herbs contained in this genus. The binomial (‘two stage naming’) system gives a precise classification of the particular plant, and these classifications are to be found Linnaeus’s two definitive original works: Genera plantarum and Species plantarum. Botanists have further developed this system into a comprehensive diversely branched family tree of classifications, which includes all known plants. The complete ascending sequence is species, genus, family, order, class and division.

The meaning of the botanical name may be indicative of the history of the plant i.e. a genus may be named after a particular botanist e.g. the Kaempferia genus of some fifty herbal species withy rhizomes & tuberous roots which includes some lesser gingers, is named after the German physician Englebert Kaempfer 1651-1716. The name may also tell something of the habit or morphological characteristics of the plant e.g. in Gaultheria procumbens L., the latter name derives from ‘procumbent’ which describes the plant’s habit. A useful publication which is the standard reference for botanical latin (& which includes comprehensive listings of the meaning of plant names) is listed below under Stearn (1992).

The Rules of Plant Nomenclature.
The rules pertaining to plant nomenclature have been set out in two publications:
The International Code of Nomenclature for Cultivated Plants (first edn 1952 – the latest 6th edn. being published in 1995)
The International Code for Botanical Nomenclature (latest “the Tokyo Code: 1993).

Plants are divided into families in which similarly related plants are grouped together basic on the clear similarity of morphological characteristics.

Families may contain one genus or a large number. A genus may similarly contain one species or a large number of related individuals – for example the Rosmarinus genus contains just two species, Rosmarinus eriocalix Jord. & Fourr. and R. officinalis L. (although some workers recognise Rosmarinus tormentosus Huber-Morath & Maire, as a third species of the genus). Variations occur within a species and these are accommodated in the following manner: a subspecies (ssp.) is a distinct variant often arising because of evolution of plant form from geographic factors, varieties (var.) have small differences in morphology, and the form (forma), has very minor differences e.g. leaf or fruit colour. Cultivars offer further evidence of diversity and according to The International Code of Nomenclature for Cultivated Plants (1980), cultivars named since 1959 should be given vernacular names, which should be in roman type within quotes e.g. “Rosa”.

Hybrid plants arising from the sexual crossing of distinct species within the same genera are called interspecific hybrids and are indicated by a multiplication sign e.g. Lavandin plants Lavandula x intermedia are sterile hybrids between Lavandula angustifolia Mill. and Lavandula latifolia Medic. Less commonly met are plants arising from sexual crossings between different genera (intergeneric hybrids). Grafting one plant onto another can also produce hybridised plant growing onwards from the grafting point: these are indicated by a + sign linking the two involved species.

Chemotypes (ct.) are of especial interest in the world of essential oils. These are marked by differences in products of secondary metabolism (e.g. essential oil composition) which can occur even in morphologically stable species, such as Chamomilla recutita (L.) Rauschert. For example, four chemotypes of Ocimum sanctum L. from the highly varied Ocimum genus were described by Hegnauer (1966): a citral-type, a eugenol type, a methyl chavicol type and a chavibetonal type. The distinguishing criteria for chemotype identification are the major components only of the essential oil from a named specific part of the plant (seeds, leaves etc.). Genetic control of essential oil biosynthesis has been investigated and a bank of knowledge now exists for specific oil-bearing plants. It is probable however that many chemotypes of common aromatic plants have yet to be properly identified.

Botanical nomenclature for essential oil definition.
It has been suggested that several parameters are necessary to more accurately define the exact nature of an essential oil:

Botanical name plus naming botanist. The botanist’s name is important because for example, the Arolla pine tree was classifed as Pinus montana Lamark (syn. Pinus cembra L.) whereas Pinus montana (Miller) is now taken as syn Pinus mugo Turra – the Mountain Pine.
Part of the plant employed. Essential oils distilled from seeds, fruits, leaves, stems, bark, roots, upper branches, trunk, heartwood etc. etc. may vary considerably in composition.
Geographic origin. Gives a likely indication of composition based on commercial familiarity of the oil from that source. For example Geranium oil Chinese from Pelargonium graveleons L’Herit. Yunnan province “E” type (summer type) was indicated as superior to the winter type, and predictably contained from 6-9% of geraniol as opposed to 2-4% in the winter type (Jian-Qin Cu 1996).
Chemotype. Chemical races may exist in many species – for example Kokkini (1992) reports their existence in virtually every Mentha species or hybrid reported. It is imperative therefore to indicate the distinguishing (which are usually the major-) components.
The CAS No. There is a lot of confusion about this system, as there are both US and EINECS-CAS numbers for many/most of the common essential oils. Further, there are duplicates and anomalies in each system, but these are slowly being addressed.

The INCI system.
The INCI (International Nomenclature for Cosmetic Ingredients) system, which can be found at http://pharmacos.eudra.org/F3/inci/incichem.htm, is a system of ingredient nomenclature in cosmetics which has been widely criticised as archaic and misleading (see for example Chaudhuri 2005). Its original intention to present universally recognised symbols representing constituent cosmetic ingredients is admirable enough, but it fails the defining parameters for clear essential oil identification above. For example Rosemary oil is called ROSMARINUS OFFICINALIS (all in block capitals) under the INCI scheme, whereas botanists have being trying to educate people for years into using the conventional binomial system - in italics, with the first letter of the genus name capitalised, and quoted with an associated naming botanist (e.g. Rosmarinus officinalis L., ‘L.’ being the abbreviation for Linneas mentioned above). Further there is no distinction between major chemotypes of R. officinalis (Soulier 1996) – camphor, myrcene-camphor, 1,8-cineol, bornyl acetate-verbenone-alpha-pinene etc., which may have implications for people trying to avoid certain components e.g. camphor is contra-indicated for several specific medical conditions.

ISO standard 4720 (2002).
There is an ISO (International Standards Organisation) standard for the botanical nomenclature of essential oils (ISO standard 4720: 2002) which lists the names of 163 aromatic commercial oil-yielding species. But on occasion, misunderstanding of the law of copyright seems to prevent more widespread employment of this sort of information - the Technical sub-Committee of the British Essential Oil Association for example, do not include this useful information in their CHIP Regulations 2004 membership guidance, since they feel “this (information) is subject to copyright”. Since this information was freely available in the public domain before ISO ever published it, and since any economic botanist or suitably experienced technical person is easily able to rapidly compile this information, surely this cannot be a consideration. It should be noted that whilst the ISO standard covers most defining points for essential oil botanical nomenclature, it does not indicate chemotypes.

Example and glossary.
Siberian Fir Needle Oil Abies sibirica Ledeb. (Fam. Pinaceae). This oil is often confusingly called Siberian Pine oil, whereas it actually originates from a fir tree common to N. & E. Russia, Siberia, Turkestan etc. Abies is a genus of Silver Firs and sibirica refers to its common occurrence in Siberia. Ledeb. Is an abbreviation of the name of the botanist Carl Friederich von Ledebour (1785-1851).

ct. or bs. - chemotype
cult. - cultivated
cv. - cultivar
exs. – dried
f or filius – son e.g. Hook f., is J.D. Hooker (son of W.J. Hooker)
fl. – it photography
fol. – with leaf
forma - form
fr. – in fruit
hort. – from gardens
infl. - inflorescence
r. – rare
rr. – very rare
sp. – species
ssp. – subspecies
var. - variety

References:
Chaudhuri R (2005) “Unrealistic Hope” Soap, Perfumery & Cosmetics 78(3), 17.

Hegnauer R. (1966): Chemotaxonomie der Pflanzen Band 4, Birkhäuser Verlag, Basel und Stuttgart, Germany.

Jian-Qin Cu (1996) "Geranium oil from Yunnan, China" Perf. &­ Flav. 21, p23.

Kokkini S. (1992) “Essential Oils as Taxonomic Markers in Mentha” in R.M. Harley & T. Reynolds (editors) Advances in Labiate Science pp. 325-334 pub. Royal Botanic Gardens, Kew.

Mabberley D.J. (1998) The Plant Book 2nd rev edn. Cambridge Univ. Press.

Soulier D-J. “The Rosmarinus Genus” in Les Cahiers de l’Aromathérapie – Aromatherapy Records No. 2 Sept 1996 pp29-35.

Stearn, William T. (1992) Botanical Latin 4th edn Timber Press, Portland Oregon 1992.