Taxonomy

Taxonomy is the science of classification. Each individual plant is a species; similar species are linked into genera, and similar genera are linked into families. In scientific notation, the initial letter of the genus name is capitalized, but that of the species name is not. Thus, Eucalyptus globulus, Eucalyptus citriodora and Eucalyptus smithii are all different species within the Eucalyptus genus. In a few cases the Latin name will appear differently, indicating that the plant is a hybrid. For instance, peppermint oil, Mentha x piperita, is known to be a hybrid between Mentha spicata, spearmint, and Mentha aquatica, water mint.

You may think that learning Latin names of essential oils is a waste of time, difficult and unnecessary. Not so. Here are some reasons why taxonomy is important in aromatherapy.

• Sometimes English names are confusing. For instance, sweet marjoram and Spanish marjoram are not closely related and cannot be substituted for each other, even though the names are similar. Sweet marjoram is Origanum majorana while Spanish marjoram is Thymus mastichina.
• If you are in America and see an oil from France with the name "Pamplemousse" on it but no Latin name, you could be unaware that this is grapefruit oil. If, however, the oil was French but had the Latin name Citrus paradiso as well, you would know what you had bought.
• In some cases, a plant oil may be obtainable from a number of species within that particular genus, but the properties of each species may be significantly different both therapeutically and chemically, and one species may be much safer than others in that genus. The *Eucalyptus* oils are an obvious example here, with Eucalyptus smithii generally regarded as the safest for children.
• In a similar vein to the above, sometimes subspecies exist which may differ in their safety and uses. For instance, Ocimum basilicum var. album (European or sweet basil) has a lower percentage of *phenolic ethers* than Ocimum basilicum var. basilicum (exotic basil) and is considered a safer oil to use than the latter.

Biologists being what they are, the situation is not always so clear cut. Sometimes a plant will be renamed as someone has discovered it is more similar to Plant A than Plant B. The *chamomiles* are particularly confusing in this way. In cases like these, it is possible that either the original name or the revised name will be found on bottles, in books, catalogues, etc. For instance, clove oil is sometimes labelled Eugenia caryophyllata and sometimes Syzigium aromaticae. Both names are acceptable, and are known as synonyms.

Chemotypes

Chemotypes, also known as chemovars, also exist. The classic example of an oil with different chemotypes is Thymus vulgaris, thyme oil. In this case, all the plants look identical so cannot be separated out taxonomically into subspecies, but great variations occur within the chemical constituents, and this is reflected in the aroma too. There at at least 6 chemical variations within this species, two of which contain principally a phenol, either thymol or carvacrol, while the others have an alcohol as the main component. The alcohol may be linalol (also known as linalool), geraniol, thujanol-4 or -terpineol. The chemotypes are written as:

Thymus vulgaris ct. carvacrol

Thymus vulgaris ct. thymol

Thymus vulgaris ct. linalol

Thymus vulgaris ct. geraniol

Thymus vulgaris ct. thujanol-4

Thymus vulgaris ct. -terpineol

Often the common names of these will be reflected by their chemotype: those with phenolic components are called red thyme, while those with alcohols are called sweet thyme. In cases where thyme is collected from the wild without regard to chemotype, it is known as population thyme. It is only by propagating plants from each chemotype. ie. cloning, that a chemotype will remain distinct. If seeds are used from a particular chemotype, there is no guarantee that the resulting chemotype will be the same as that of the parent. These plants are also known as population thyme.

Rosmarinus officinalis, rosemary, and Salvia officinalis, sage oil, also have several chemotypes associated with them. As with the thyme oils, each of these will have a specific therapeutic picture depending on the principal component.

The chemotypes of rosemary are cineole, camphor and verbenone, with cineole regarded as the safest and verbenone the chemotype that is contra-indicated in pregnancy and with children. Sage is commonly known as a toxic oil because it contains up to 60% of thujone, a toxic *ketone*, but a low-thujone chemotype is also available which is much safer.

The chamomiles

Three different chamomile essential oils are available: Roman chamomile, German chamomile, and Moroccan chamomile. Despite the similarity in common names, the recognized Latin names are from different genera.

Roman chamomile is known as Anthemis nobilis and Chamaemelum nobile.

German chamomile is known as Matricaria recutita or Matricaria chamomilla.

Moroccan chamomile can be known as Ormenis multicaulis, Ormenis mixta or Anthemis mixta.

In this case, it may be less confusing to call the oils by their common names. The chemical constituents of these oils vary and the oils also differ therapeutically, though to an extent there are similarities with all three oils.

Orange oils

Latin names are particularly important when describing essential oils from the bitter orange and sweet orange trees. Sometimes an oil may just be labelled "Orange oil", but this is inadequate. The Latin name of the sweet orange tree, also known as orange portugal, is Citrus aurantium var. sinensis, while that of the bitter orange, or orange bigarade, is Citrus aurantium var. amara. Sweet orange is considered a milder oil than bitter orange, and is more suitable for children. With orange oils, it is also important to state what part of the plant the oil is coming from, ie. if it is from the peel, leaves, flowers or a combination of the leaves and flowers. Neroli and petitgrain are usually distilled from the flowers or leaves respectively of Citrus aurantium var. amara, but occasionally Citrus aurantium var. sinensis is used instead. However, neroli from the sweet orange tree is considered to be less therapeutic.

Lowana Veal is a biologist who has carried out experimental work with essential oils. She has also written a number of articles on complementary health issues.

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