SCENTS OF IMPORTANCE
by Alan Gray

The sense of smell usually is considered to be rather poorly developed in humans. Perhaps it may be more accurate to suggest that as one of five senses, smell is becoming redundant. While the above suggestions may be matters for argument, it is certain that smell still is very important to most humans and for many it is a most evocative sense. Instant memories of past events are often triggered by a vagrant whiff or the chance meeting of a smell experienced long ago. Smell also is very subjective - what is a pleasant fragrance to one may easily be quite unpleasant to another. This is very true when it involves our appreciation of the aromas and smells produced by many plants.

Bedfordia linearis
                   Bedfordia linearis    
                     Photo: Alan Gray
Flowers appear to have an important purpose in the production of a perfume, pleasant or otherwise, and that is as an attractant to those insects, birds, or small mammals which serve to spread the pollen from one flower to another as part of the reproductive process. Of course, the insect would seem only to relate the perfume with a source of food such as nectar and hardly with the intention of playing Cupid to the flower. It is interesting to contemplate the reasons why some plants appear to produce nectar but have no apparent perfume, for example Ranunculus (buttercups) and many of our native heaths, the Epacris species. Perhaps they have scents but the human nose cannot detect them?

The presence of aromatic substances in the leaves, bark and other tissues of plants is not as easily explained. Plant scientists seem to agree that most if not all of the substances or complex chemicals which give many plants characteristic odours and perfumes are the by-products, even waste products, of plant metabolism. These chemicals and the smells they produce can be very characteristic of certain plant families, for example, the "carrot" smell of the Umbellifer family, and the Eucalyptus smell of the Myrtaceae. Other characteristic smells such as the citron smell of the citrus family, Rutaceae, can be a little deceiving, for not only is this distinctive smell so prevalent in that family, but it also occurs in a species of eucalypt, a species of grass and a member of the mint family all of which are quite unrelated. Perhaps the fragrant oils and other odiferous chemicals in many plants may act as deterrents to browsing animals and insect predators.

However, those who have ever wondered why it is so difficult to find a whole Eucalyptus leaf unchewed by insects and those who reflect that koalas and in many cases possums feed almost entirely on Eucalyptus leaves might not entirely agree with that theory. A high oil content in the tissues of such delicate organs as leaves or needles may well be an advantage in plants which must contend with severe winter temperatures. Many oils and resins do not solidify until temperatures reach well below zero. Their relative abundance in cold-country plant tissues might prevent otherwise severe damage as would certainly occur in water-saturated leaves.

On the other hand how does this affect relatively warm-country plants such as the Eucalypts with their oil-laden leaves? The oils and other chemicals which give many plants their unique perfumes and odours are not necessarily simple in their chemical recipes nor do they often occur as a single cornponent of a smell. A good example of a very complicated plant perfume is that of the well known and very popular native plant, the Australian Brown Boronia (Boronia megastigma) where more than 20 different and often complex chemical ingredients combine in various proportions to produce the exquisite perfume produced by this plant. To smell a flower one only has to either catch the scent wafting on the breeze or to invade the privacy of the blossom with one's nostrils. In the majority of cases a flower's perfume is far more delicate and enjoyable after having been diluted with the right amount of air rather than being taken “straight" only millimetres from the flower. A good example of this is again, our Brown Boronia.
The diluted scent is by far the most exquisite and enjoyable.

Perhaps now we might look at a number of Tasmanian plant families within which are various species having leaves, bark or roots with perfumes, nice or not so nice, with all due respect to the profound subjectivity and hence the difficulty in describing a "smell".

Tasmannia lanceolata A familiar plant to most bushwalkers is the so-called Mountain Pepper (Tasmannia lanceolata). The leaves and bark of this plant give off a spicy aroma, pungent
aroma when crashed or bruised, and the "pepper" description is very apt for, as those who have been caught know, chewing the leaves, bark or berries produces a hot, peppery
sensation on the tongue and lips. Strangely, if one has a sassafras leaf handy, chewing this will nullify the burning sensation produced by the Mountain Pepper.
Perhaps the best known for their smell here are the Boronias, Eriostemons (currently Philotheca) and Zieria. None of the six or so species of Boronia can lay claim to a flower perfume anywhere nearly as exciting as the Brown Boronia discussed earlier. The Lemon-scented Boronia (Boronia citriodora), or, as it is often called, Lemonthyme, is abundant in the West and South-West and is famous for the refreshing, almost sweet, citrus fragrance which arises when the leaves are crushed between the fingers or underfoot. 
Boronia anemonifolia
    Photo Launceston Field 
   Naturalists Club
Less well known is the very warty-leaved Boronia properly known as B. anemonifolia. ("Stinking Boronia") The foliage of this shrub when crushed leaves the fingers sticky and as Dr Winifred Curtis has described, "smelling strongly of turpentine". It may as well be explained here that the turpentine smell refers to the natural “oil of turpentine” and not the mineral sort now used as a paint thinner. Of the two Philocatheca, or Wax flowers, in Tasmania, P. verrocosus has very warty, glandular leaves and when crushed emits a sharp but not unpleasant smell somewhat similar to turpentine but with a sweet and spicy citrus “after-smell”.
Another of the Rutaceae family with a distinctive smell is Zieria arborescens, appropriately also known as Stinkwood.  Although an underlying background of citrusy odours is detectable, a combination of these with other oils etc. gives the crushed leaves of this plant an often strong and unpleasant odour, certainly not one for "my lady" to dab behind her ears.    Photo Launceston Field Naturalists Club
Zieria arborescens
Another group, all members of which are known for their oils and smells, is the Myrtaceae family,  most famous of course being the genus Eucalyptus. With well over l00 species in this genus, an article on this group alone could he written so only a brief mention can be made here. Of the three groups which occur naturally in Tasmania each can be recognised by certain oils and their particular odours. Most would be familiar with the Eucalyptus oil which can he obtained from the chemist and which, when sprinkled on to a handkerchief, is of value in clearing a stuffy nose. This is an essential oil called cineole and is
characteristic of the group of eucalypts which include our blue, white,  yellow, spinning and cider gums, among others.
Eucalytus delegatensis Another group, the peppermints, are characterised by an oil known as piperitone, giving their leaves the fresh, "crispy" aroma which lingers on the fingers after the leaves have been crushed. The stringybark and ash group presents other combinations of essential oils which give off rather  earthy, sweetish smells, among the other aromas.  One eminent professor of botany once described the smell of Gum-topped Stringy bark (Eucalyptus delegatensis) as akin to the aroma of unwashed bushwalkers' armpits.  Here lies the subjectivity of smell interpretation. I think that this eucalypt has rather sweet-smelling leaves.
Photo Launceston Field Naturalists Club

Each of the above three groups also shares similar oils with each other. It is the combinations of  these oils, along with the preponderance of one or others in particular, which produces the characteristic odour of each group.Also in the Myrtaceae and possessing various combinations of essential aromatic oils are the Melaleucas, Leptospermums, Callistemons, and Baeckeas, to name a few, and all possess distinctive aromas which arise from the essential oils in leaves and bark.
A familiar group of plants to most is the Umbellifer family, the Apiaceae, from which we obtain important food and flavouring plants such as carrots, parsnips, celery, parsley, carroway, and fennel.  The distinctive "carroty” smell is due to various oils in the plant tissues. Many of our native plants can be identified by this smell as belonging to this family. One, such as the little sea parsley (Apium prostratum) is common on many a coast and shoreline and presumably would have been gathered and eaten by the Tasmanian Aboriginals.

Olearia argophylla
   Photo Launceston Field 
  Naturalists Club
The very large daisy family, the Compositae or Asteraceae, also has in Tasmania a few notable plants with aromatic leaves or bark. One, the familiar musk (Olearia argophylla), presents a very faint but delicate fragrance on crushing the leaves. It is "musky" to the
nose but never strong and soon dissipates, leaving an earthy "flat" after-smell.  As with so many other leaf and bark tissue smells, it is quite important to sniff gently while crushing or robbing the source of the smell, not by crushing at arm's length then bringing the
subject to the nose, by which time the often volatile oils will have evaporated and gone.
The large genus Ozothamnus, well known as the everlasting daisies, contains a group of shrubby plants often referred to as kerosene bushes. Their leaves, twigs, and other parts plants exude a sticky substance which, on a warm day produces a delightful aromatic-sweet fragrance much "sweeter" than kerosene but nevertheless something akin to it.The two species most notable for this lovely mountain-top aroma are Ozothamnus ledifolium and O.ericeteum. Interestingly,  the flavouring we know as curry is obtained in
part from a species of Ozothamnus.

The genus Senecio (the fireweeds and groundsels), have in Tasmania two notably aromatic plants. The first, S. linearifolius, the very common plant almost weedlike in its invasive habits and often called fireweed due to its rapid colonisation of !and cleared by fire, is quite aromatic but not in a pleasant fashion. One of the closest descriptions of the smell of this plant is like boot polish. Twigs of this plant placed around desirable garden plants are said to repel the attentions of possums. Another Senecio (now properly known as Brachyglottis brunonis) is found only on Mts Wellington and Dromedary. Rather than a small shrub, as is common for Tasmanian Senecios, this plant of very restricted distribution grows into a small but distinctive tree. The buds and new leaves are commonly covered by a sticky exudate which smells strongly of the old remedy for many ailments, Friar's Balsam.

Our very widespread and common Bedfordia species, also known as "Musk", "Dogwood", and lately "Blanket leaf”, has a claim to aromatic fame. The bark, and to a lesser extent the leaves, produce a very sweet musky aroma almost honey-like in its delicate pungency. After rubbing pieces of cut bark this smell will remain on the fingers for quite some time.

The mint family, or Lamiaceae, is famous for the many plants which produce so many of the flavouring substances and culinary herbs in use throughout the ages. In Tasmania, three native species of the mint bushes (genus Prostanthera) have aromatic foliage, the smell of which leaves one in no doubt that it is related to the true mints. Prostanthera lasianthos in particular is well known for its sweetly aromatic leaves. Often called native lilac (no relationship) or Christmas bush, though more appropriately mint tree, it is found growing in abundance in damp forests and along creek banks.

No mention of plants with aromatic leaves or bark would be complete without reference to our Southem Sassafras (Atherosperma moschatum). The spicy, fragrant aroma of the leaves when crushed, which also is contained in fresh bark, is well known to many. So pleasant is the fragrance that there are many recipes for incorporating its aroma into various tea and beer brews.

Little mention has been made of those few plants which produce odours or smells in their leaves and elsewhere which are considered to be less than pleasant or even intolerable. Apart from those already mentioned, Stinkwood and the Boot polish fireweed, two others stand out. First is a small tree belonging to the Waratah family, commonly known as the native plum (Cenarrhenes nitida), which is pleasant to look at but to smell the crushed leaves is another matter. Dr Winifred Curtis describes these as "foetid when bruised". Many bushmen describe them otherwise in terms which would be indelicate to repeat here.

Quite similar but with a less potent pong are a nmber of shrubs which belong to the Rubiaceae family, and includes such well known plants as those which produce coffee, quinine, ipecacuanha and the fragrant ornamental plant the Gardenia. Our smelly native representatives include a couple of  inconspicuous little herbs known as Opercularia which when bruised emit a fairly strong unpleasant smell.

Other smellies belong to the Coprosma genus, also known as Native Currant and Coffee Berry. In some species the foliage when crushed gives off a rather unpleasant smell. The genus Coprosma is a name translated from the Greek root quite literally meaning “with a smell like dung”.

Finally, a mention of some other plants with famous or interesting smells:

Those who have potted or otherwise handled the roots of small Acacia or wattle plants will be aware of the rather strong, (almost foetid) smell produced during handling. This probably arises from the activities of the nitrifying root bacteria nodules common to most leguminous plants and some others. To me it is a sign that all is well and that the bacteria are doing their good work.

Our well known and fairly common East Coast conifer, the Oyster Bay pine (Callitris rhomhoidea) is a pleasure to handle while potting or planting out. The bruised roots of this plant and its ilk give off the most pleasant refreshing, spicy aroma imaginable. It's almost mouth watering.

Last but not least we must mention a famous plant smell, one uniquely Tasmanian. What true Tasmanian does not smell with pride as well as with some feeling of respect the delightful aroma of the freshly cut or worked timber of our Huon pine. This aromatic, somewhat musty, but "sharp" smell is due to a combination of many oils and fragrances contained within the timber. These oils, the most abundant of which is known as methyl-eugenol, impart this timber with its unparalled durability and special charm.

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