Fragrance of Leaves
 

Just been outside tidying my garden and beating some lemon thyme into submission. While doing so I began to wonder about the lemon fragrance that many unrelated plants have (Eucalypts, lemon grass, lemon thyme, lemon balm and of course lemons). Do all these plants contain the same compound which creates this smell, or are unrelated chemicals involved that just happen to have this lemon property?

What other odours do plants have like the above examples? I was thinking peppermint, (mints, pelargoniums etc.), anybody want to add to the list or have other fragrances in mind?

The main compound common to the lemon scented plants is citral, an aldehyde. It occurs in admixture with other chemicals though. It reaches quite high levels in lemongrass.

Another lemon scented plant that springs to mind is Backhousia citriodora.

The odour components of plants are widely spread across different species. As an example, the local ti-tree here, Taxandria, has an oil that is a mixture of eucalyptus (cineole) and lemon (limonene) yet it smells like neither of those.

Thanks morrie.

I guess if us humans were blessed with a better sense of smell we could discern the differences in odours far better. Lemon balm and lemon thyme smell much the same to me, but I guess an animal like a dog would notice them being quite different.

The sense of smell is an odd thing. People smell things differently and there is a definite emotional association that comes into play. Dogs have sensitivities that vary between a thousand and a million times our own.

Lemons, to my nose, don't have a particularly strong 'lemon' smell. The main oil in them is limonene, which is common to the citrus oils and it just has a little bit of citral.

I have been interested in plant aromas for as long as I can remember. When I walk though the bush I am constantly picking leaves from any plant that is unfamiliar to me and smelling the crushed leaves.

There is a good book on the aromatic plants of Australia by Wriggley and Fagg (who else!). The describe a wide range of plants and their smells, but they don't go into the chemistry. I recommend it to anyone interested in the subject.

I notice that the Rutaceae rank highly amongst the aromatic plants.

Some of the minor components of the chemicals in plants can have significant effects. For example, small amounts of indole promote the powerful smell of jasmine, but it doesn't actually smell of jasmine itself. And in fact it is present in faeces!

To me, Melissa officinalis is definitely different from Lemon scented Thyme. and it is present in faeces Yeah one of my ex-bosses would always say .. quick, package that up and send it to the perfumery.. whenever he farted.

Thanks for heads up on the book (you just reminded me I have a copy of Wrigley and Fagg's Eucalypts on lay-by, better go pick it up).

Rutaceae certainly are aromatic, we have Zieria smithii in abundance in "my" little patch of bush. Many people find it 'orrible, but I don't find the smell that offensive.

Years ago I borrowed my Dad's car to do a trip to Canberra and decided to take the back road through Captain's Flat and Araluen on my return journey. Spotted a Prostanthera species I'd not seen before and thought I'd grab a heap of material for cuttings. By the time I made it home the car stank of the stuff and even after removing it the smell lingered for weeks (the bits of plant I grabbed got placed in a plastic bag and didn't come in actual contact with any part of the car interior, so it must the fumes/volatiles (or whatever correct term is) getting into the carpet. Dad was not impressed with me.

That touches on another factor relating to plant smells and chemistry in general. There can be very wide regional variations. That is true of Zieria, but applies to many many plants. A classic example of such variation is Pituri.

regional variations can come down to position relative to.. and this may be sun, shade, warm surface or cold surface of soil/rocks/gravels/sands.. soil moisture.. season.. and etc.

A bit off-topic, but...

Not a plant I'm familiar with personally (but do know what it is and one of its uses!!!). A bit of a coincidence as it was only a few days ago I was listening to one of Richard Fidlers Conversations and he was chatting to an aboriginal woman by the name of Keelen Mailman who mentioned that whilst working as a park ranger and showing tourists around, it was always Dubosia that attracted the most interest...

"uses" relate to what indigenous people used it for.. not what 'whiteys' think it was used for.

Too cryptic for me RB, I'm a just a "whitey" reporting what was said by an aboriginal lady.

Edit: The name Pituri refers to the plant product, the plant itself is Duboisia

Quite a few Asteraceae (daisy flowers) have highly aromatic foliage. One in particular is the introduced weed Dittrichia graveolens (syn. Inula graveolens) or Stinkwort and boy does it stink. No need to crush the leaves on that one and if you pull one up your hands hum with its odor for ages.

In the dryer interior, highly scented plants tend to be more common, which extends to many plant families. Most of these plants have glandular hairs that exude a sticky substance, which besides the objectionable odor are usually tacky to touch. I would say the main purpose of these glandular hairs is to deter grazing animals and in Australia besides current day macropods, the now extinct megafauna were probably massive feeders on the vegetation and probably simulated these plants defense mechanism.

Sorry Woolly. I didn't mean it to sound odd. If you know, you know.

.. many closely related to Pyrethrum

possibly the best known would be Chamomile

Asteraceae wouldn't have been a family to immediately spring to my mind, but on pondering it and considering the sheer number of genera and species, it certainly makes sense to me (now) that there would be numerous "stinky things" amongst them.

Ambrosia tenuifolia and Ambrosia psilostachya.. are two I'd mention.

Yep. The more I've thought about members of Asteraceae, the more I realise how neglectful I was in not really considering the family.

Tagetes minuta - Stinking Roger popped into my head, and if I were to go through a list of culinary herbs I'm sure I could think of heaps.

Well stinking rogers, are marigolds..

Another lemon scented one , which reminds me of lollies is Lemon verbena, Aloysia citrodora , small shrub to a couple of metres, depending on where you live.

Also the Basil genus, Ocimum sp. has a vast arrray of different scents, Menthol, lemon, cloves, mint, lime...and the list goes on and on.

Then there are the Pelargonium sp. they have , orange, mint, lemon, rose, etc,. etc,.

I too like Woolybutt am intrigued as to how all these varying Genera of different Family have similar scents??

Interesting topic !