[neilep (OP)]

Dearest Sirs et Madames de Scientifique Luf

This is a Lemon grass plant :

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This is some Lemon luff :

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What me wants to know is, was  there any time when the a lemon slipped off with a grass plant for some flora fornication and voila !!...the result was the Lemon Grass above !!

Or is it just a coincidence that the two have similar citrus flavours  ?

Presumably the lemon came first before the Lemon Grass ?...and I assume they are two completely different species..?

[Karen W.]

 I believe you are  right, Down In my yard I have arather staggely lookin Lemon Verbenia bush that looks more like a dying tree.. You can use the leaves in tea with mint it! The leaves smell like lemons also. If you rub or crush the leaves in your hand the fragrance is outstanding..surely this was a manege et trois!

[elegantlywasted]

Is it possible the the citrus flavour and scent are a defense mechanism, a deterrent for animals and insects. Most domesticated animals hate citrus scents so I'm assuming non domesticated ones do as well. And that a smart person came along and just decided to name it Lemon Grass because it reminded him/her of lemons? And that there is no correlation between lemons and lemon grass?

[Karen W.]

 That's interesting.. They sure smell nice anyway.. Does the lemon grass smell of lemons  as well?

[neilep (OP)]

Is it possible the the citrus flavour and scent are a defense mechanism, a deterrent for animals and insects. Most domesticated animals hate citrus scents so I'm assuming non domesticated ones do as well. And that a smart person came along and just decided to name it Lemon Grass because it reminded him/her of lemons? And that there is no correlation between lemons and lemon grass?

Hi Meg,

Excellent points Megn......the defense mechanism is a really strong contender.....in the case of lemons...do they smell strong enough to put off a hungry bear etc ?...hmmmm....cos they taste about a zillion times more than their smell..and once bitten..I presume it's bye bye lemon !!...but..then the rest are rescued...Hmmmm !!....wow..martyr lemons..LOL !

[neilep (OP)]

That's interesting.. They sure smell nice anyway.. Does the lemon grass smell of lemons  as well?

I am sure they do.....I get them a lot in my Indian and Chinese meals...of course by the time they reach my tummy they are like ...well heated up !!

[Karen W.]

COOL..I like lemon things... YUM..

[Karen W.]

 Sir, off subject what is that big beautiful plant above your lemon grass!

[neilep (OP)]

Sir, off subject what is that big beautiful plant above your lemon grass!

Karen Mam..I have no idea...It is the picture I blatantly stole from Wiki's entry on lemon grass http://en.wikipedia.org/wiki/Lemon_grass

lol

[Karen W.]

LOL I was assuming it was part of your landscape..LOL It is a cool broad leafed plant.. I do so love those kind makes me really want to go to the jungle and visit the real thing... All that lush lovely greenery!! Tropical heaven tropical rain forest.. wouldn't that be cool to really visit a rain forest with plants like that??

I like the lemon grass, I think that might look nice by the pound and smell nice also if they have lemon parfume!!!LOL

[neilep (OP)]

LOL...me wonders if there is Lime Grass and Orange Grass ?

[Karen W.]

Perhaps.. There is we should see! I like the ornamental grasses!

[WylieE]

What you are detecting when you smell a lemon or lemongrass is a combination of terpenes and their derivatives, volatile compounds produced by plants.  Most plants (if not all- I don't know of any that don't) produce terpenes.  It is the combination of the volatile compound produced by plants that give them their unique smell.
They are produced from a very old pathway that is highly conserved in plants.  This is a perfect example of how old this pathway is- lemongrass and the lemon fruit tree are very distant evolutionarily, but they both have this pathway.  However, the product you detect in each case is slightly different.

In the case of lemon grass the oil is mostly citral with a bit of limonene and other components.
For Lemon (the fruit) it is mostly composed of limonene and a bit of citral

You can see (if you can look past the lopsided drawings) that the two compounds are pretty close and that might explain why the smell similar. 

[diagram=112_0]                         [diagram=113_0]
Limonene                                                                       Citral

Another plant that produces a lemon-like combination of these is Leptospermum citratum (Lemon tea tree) this has mostly citral and smells VERY “lemony”

The function of terpenoids varies widely: some serve as insect attractants, some serve as insect repellants, some serve as communication both within a plant and between plants. 
In fact, sometimes, the same terpene can have different functions: 1,8 Cineole in flowers is an insect attractant, bringing in pollinators, but 1,8Cineole and Camphor  act as feeding deterrents to deer. 

Limonene and its derivatives (limonoids) like peppermint and spearmint are thought to be anti-herbivory compounds due to their bitter taste.  Although, I sure love the mints – obviously not a good anti-herbivory compound- but looks like it is working in the plant's favor anyway- if you see all the mint fields around here.   


How the terpene product is "decorated" at the end and this gives rise to a wide number of different products.  These products are very useful to humans and understanding their production and the variety of compounds produced is an active area of research. 

Other related terpenes that you may recognize:
Patchoulol (especially if you know any old hippies)
Carveol (think spearmint)
Citronellol (keep those mosquitoes away- also found in roses and geraniums)
Pyrethrin I (an insecticidal produced by Chrysanthemums)
Taxol (an anticancer drug)
Digitoxigenin (a precursor to digitoxin, the heart drug- comes from foxglove)
Tocopherol (Vitamin E)
Ecdysone (disrupts the insect molting cycle)
Menthol
Pinene (the principle component of turpentine mmm smell that pine forest smell, also toxic to bark beetles)

Colleen

[neilep (OP)]

Wylie E.

Oh my !!...

I couldn't have asked for a more concise answer to my question.

THANK YOU so much for this and for the effort in writing it here and the drawings too.

THANK YOU....COLLEEN.

[WylieE]

Hee Hee,
 Thanks, I'm really glad you appreciated the drawings. . .they took way longer than they should have, so it is good to know they were worth the time.
It is no problem, actually, I should thank you- you are helping me procrastinate and it was fun.

[Karen W.]

Cool!