Rhona Wells investigates the curious and sometimes offensive world of the Titan arum flower and its relatives
Not all fragrant plants are a pleasant experience, as epitomised by the Titan arum flowering at Kew from 4 August this year. Its flowering was brief - two days of full bloom - but its scent spectacular! Once smelt, never forgotten.
The Titan is also known as the corpse plant, so-called because of its fragrance. In Indonesian it’s bunga bangkai, bunga meaning flower and bangkai meaning corpse. For the same reason, this same name is also attributed to Rafflesia which, like the Titan arum, also grows in the rainforests of Sumatra.
The Titan arum originates in the moist shaded rainforests of Sumatra. The first European botanist to encounter it was the Italian Odoardo Beccari, who was travelling in the region in 1878. He sent back seeds to his patron in Italy and one of the young plants that germinated from them was subsequently dispatched to Kew where it flowered in 1889, exciting great public interest. In 1926, when it flowered again, the crowds attracted by the phenomenon were so large that the police were called in to keep control. More recently, in 1996, a Titan arum flowered at Kew for the first time in many decades, but then 2002 saw an unprecedented three flowerings in as many months, with a further flowering later that year, three more in 2005 and the latest on 4 August 2006.
Titan arum is a member of the family Araceae, the Aroids or Arum plants. Members of this family include the calla lily, Jack-in-the-Pulpit, anthuriums, dieffenbachia and philodendrons. With its huge flowering structure, known as inflorescence, rising up to 3m above ground and its single immense leaf, Titan arum is, as its name suggests, a giant among plants. It grows from a large tuber that can weigh over 170 pounds. Thousands of flowers are hidden inside at the base of the spadix, the fleshy central column. The large, frilly-edged, leafy skirt enclosing the spadix is the spathe, which when open resembles an upturned, fluted bell with a crimson interior. Only when the spathe is completely unfurled are the flowers mature.
Odours foul & fair
The Titan arum heats up during its bloom. The interesting smell that these corpse flowers are famous for is composed primarily of fairly heavy, sulphur-based compounds that do not easily become airborne. The plant heats itself in order to volatilise its scent, enabling the smell to go further, attract more flies and increase the chance of pollination. To heat up, the plant burns stored carbohydrates, short-circuiting its basic respiratory process in order to maximize the production of heat. Many members of the Arum family perform metabolic burns like this, albeit on a smaller scale. Unfortunately, the enormous amount of energy the plant expends in attracting flies limits the amount of time it can bloom, which explains why these plants typically bloom for only a few days, and why they don’t bloom every year.
Many of the 170 or so species of Amorphophallus produce a variety of obnoxious odours ranging from rotting meat, dung and rancid cheese to a nauseating gaseous stench. Size does not always equate to ability to generate a stink. Relative to A. titanum, the inflorescence of A. bulbifer is small, yet the gaseous stench it produces can make working in a glasshouse with it a sickening experience, as Kew staff can testify.
Some Amorphophallus species, however, produce pleasant odours. For example, A. haematospadix smells of bananas while A. dunnii has the odour of freshly chopped carrots.
The major components detected in the carrion and gaseous odours are the sulphur-containing compounds dimethyldisulphide and dimethyltrisulphide. The banana odour of
A. haematospadix appears to be due to isoamyl acetate while the carrot odour of A. dunnii consists almost entirely of 1-phenylethylacetate, according to the researchers at Kew. The chocolate odour of A. manta has yet to be analysed.
Scientist Geoffrey Kite from Kew’s Jodrell Laboratory has investigated the obnoxious smells that they produced. The strongest smells occurred on two consecutive evenings, firstly when the female flowers were ready for pollination and then when the male flowers were ready to shed their pollen.
One aim of the work at Kew is to compare the chemical nature of the odours with a modern classification of the genus based on DNA sequencing and a full scale morphological analysis. The few observations available are for foul smelling species and these seem to attract carrion beetles. This is in accordance with chemical data on the odour; dimethyldisulphide is known to attract carrion feeding or breeding insects and is used in a commercial lure for screw-worm flies. The chemical constituents of the odours might also provide clues to the pollinators of these plants since, for most species, the pollinators remain a mystery. An interesting adventure into smell, though probably not the next best seller.