It is my birth month and the middle of spring, what is not to like about October in Australia? Well to be honest it didn’t start out so well, over three months without any rain of note was taking its’ toll, and the colour of the landscape was gradually turing brown. However the spring rains finally arrive in the second half of the month, providing green pastures and an abundance of flowering trees, vines and blossoms of all kinds.
Along with the regular October colour spectacle provided by the silky oak and jacaranda trees, most of the Melaleucas are also providing a show of creamy-white blossom, the most outstanding being the “snow in summer” Melaleuca linariifolia, one of only two species used as a source of authentic tea tree oil.
Last week saw me travelling up from the Hunter Valley to Tweed Heads on the Queensland border to speak at the Aromatica Conference, and while the white flowering Kunzea ambigua was a dominant roadside specimen along the M1 motorway during the early stages of the trip, further north the Melaleucas took their place. Having stopped at a friends tea tree plantation to collect some oil and plant specimens of Melaleuca alternifolia, I was able to use my variously gathered specimens to illustrate the topic, “Know your Chemotypes and Australian essential oils”. The fact is that to meet world and Australian standards for tea tree oil, not only does it need to come from one of the two species referred to above, it also needs to be the correct chemotype, ie with a chemical profile with minimal levels of 30% terpinen-4-ol and maximum levels of 1,8-cineole. Other chemotypes of the two species have essential oil profiles with much lower levels of terpinen-4-ol and higher levels of 1,8-cineole. These are still great essential oils, but they can’t be marketed as tea tree oil, so there is naturally much less attention paid to them.
I was able to produce specimens of the authenticated chemotype of M. alternifolia I’d just collected at the tea tree plantation, whereas the M. linariifolia specimen was collected from the wild, and could have only be authenticated in a lab by GC analysis. The point of circulating the two specimens around the room during my talk, was to see whether the two could be distinguished using the human sensory apparatus ie the nose! In my opinion the two specimens were clearly different, hence it is unlikely the M. linariifolia specimen could produce genuine tea tree oil, however I believe that it produced the most pleasing, more floral aroma compared to tee tree oil – often tagged as being a “medicinal” smelling oil.
Along the banks of the Brisbane river where I am currently staying, tea trees are also in bloom, however there are mainly the sweet smelling M. bracteata. This species is popular for planting, however the oil it produces is high in phenolic ethers, some of which may be toxic or even hallucinigenic. To me it has one of the least pleasant odours of the Melaleuca genus.