Tuesday, 4 February 2014

Wormwood, revolutionary but not revelationary


The main thing you'll taste in the green liqueur absinthe is a licorice flavour, thanks to anise, not the mystical wormwood ingredient. But there is some wormwood, Artemisia absinthium, in it still. Vermouth also has a little wormwood, added originally to wine to disguise the less attractive qualities of cheap alcohol (according to my Drunken Botanist companion book, by Amy Stewart).

Although (again thanks to Amy Stewart) the active and potentially dangerous chemical thujone is present in old and new absinthe, and regulated in some countries, plants like Sage have even higher doses. The wild nights and hallucinations attributed to absinthe are more likely due to the wildly high alcohol content of the drink - about twice as strong as gin.

A few different species of Artemisia are used in alcoholic drinks, collectively called génépi after one of the other species used, Artemisia genipi. Artemisia absinthium is a European plant but one that has established itself nicely in places like Mexico.


That's the wild and crazy side of wormwood. There are about 400 hundred species of Artemisia but for many of us we know the genus by a handful of tough and persistent hedge species.

Most of the wormwoods I could track down in the Royal Botanic Gardens were Artemisia arborescens but we have plenty of other species and cultivars. Artemisia 'Powis Castle' (an excuse to top this post with a picture taken on my visit to the Welsh Powis Castle in 2012). I couldn't find but we have records of it from the Grey Garden (near the Temple of the Winds) and the Herb Garden - it's probably pruned back or covered by some other grey or herby species.


I read recently (Landscape Architecture Magazine, October 2013) about Artemisia annua, described by the author Constance Casey as 'perhaps the least-impressive-looking of the several hundred Artemisia species'. So it wasn't in the magazine for its landscape qualities!

It's profile links back to my November post about quinine and malaria. The chemical responsible for some of the bitter attributes of the Artemisia leaves, and part of its weaponry against nibbling bugs, is a sesquiterpenoid. Sesquiterpoenoids are interesting molecules: the most widely used antimalaria drug in use today, called coaterm, contains a sesquiterpene extracted from  Artemisia annua.

This powerful ingredient was discovered by Chinese scientists working under on the order of Mao Zedong. They screened 2000 traditional Chinese medicines, testing 380 extracts. But the clue was found in a book written during the Han Dynasty (over 1800 years ago) which recommended wormwood for treating 'intermittent fevers', a symptom of malaria.

Artemisinin was trialed on mice, then self-administered by the researcher, Tu Youyou. Apparently all survived and the drug was used in China in the 1970s, taking longer to reach the rest of the world due to China's isolation during the Cultural Revolution. So a good news story, luckily. Tu Youyou still lives and works in China today according to Casey.

There are sure to be other useful (to man and mouse) ingredients in the chemical cocktail within wormwoods. Meanwhile they provide a handy plant for drought-stressed gardens in Melbourne. So tough they sometimes stray beyond the walls. Artemisia arborescens, the Silver Wormwood, has become naturalised in New South Wales and South Austalia but although persisting around old gardens in Victoria it isn't yet (as far as I know) considered to be a worrisome weed. The Chinese Wormwood, Artemisia verlotiorum, however, is, particularly on roadsides around Melbourne.


2 comments:

mr_subjunctive said...

Minor technical quibble:

"Sesquiterpinoid" is a generic term, not the name of a specific molecule. (Sesquiterpene: a hydrocarbon molecule with three connected groups of five carbon atoms, arranged in a specific way which is called an isoprene unit. Sesquiterpenoid: a sesquiterpene with other atoms attached to it, usually oxygen.) It makes sense to say a plant contains a sesquiterpene (in this case artemisinin), or that a plant contains sesquiterpenes, but not to say that a plant contains sesquiterpene.

Tim Entwisle said...

Thanks, I appreciate that correction. I'm used to talking about carotenoids and carotenes in algae but probably got the grammar wrong there too! Hopefully all fixed now in this post... Tim