Titan arum

Odours: foul and fragrant

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 their 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 staff at Kew 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.

Odours have been used to classify Amorphophallus species in the past, but the human nose can be deceived. When plants in the Princess of Wales Conservatory flowered in 1996, 2002 and 2003, scientist Geoffrey Kite from Kew’s Jodrell Laboratory 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.

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; the chocolate odour of A. manta has yet to be analysed.

One aim of the work 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 chemical constituents of the odours might also provide clues to the pollinators of these plants since, for most species, the pollinators remain a mystery. 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.

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