The beauty or the beast?

By: Marcelo Sellaro - 07/11/2011

The titan arum is not the sort of plant you can be neutral about. It is curious, weird, rather obscene, revolting and even terrifying. Scientifically known as Amorphophallus titanum, it is by no means easy to tell that it belongs to the Araceae family, which includes the ‘Swiss Cheese Plant’ (Monstera deliciosa) with its unmistakeable foliage, the virginal ‘White Arum’ or ‘Calla Lilly’ (Zantedeschia aethiopica), the ‘Flamingo Flower’ (Anthurium andraeanum), and the ‘European Arum’ or ‘Lords-and-Ladies’ (Arum maculatum and A. italicum).

The flower of Amorphophallus titanum is indeed very odd. It consists of a single bract (modified leaf) called a spathe, which provides cover for a central flower-bearing protuberance, the spadix. This floral peculiarity is technically an inflorescence, not a flower; the real flowers being tiny and protected at the base of the spathe. The shape of this inflorescence has inescapable sexual connotations beyond the fact that it is the plant’s reproductive apparatus.

Inflorescence of the titan arum

How we grow them at Kew

The titan arum is a tuberous species that characteristically has dormant periods when leaves are not present, and these normally correspond to the dry season (or winter) in the habitats where it grows. At Kew, we grow them in huge containers that hold tubers which can reach up to 90 kg. The leaf is a marvel in itself and at first glance resembles a sapling tree. It is patterned with irregular pale green blotches, which at a distance render it indistinguishable from the moss and lichen encrusted on the trunks of surrounding trees. At the apex it divides into three, and then again into several more divisions, making an umbrella of leaflets about 7 m in diameter.

 

Titan arum in the Tropical Nursery at Kew

In the Tropical Nursery at Kew, Amorphophallus titanum is not very difficult to grow, provided a number of conditions are met. These are roughly: a rich soil and trace elements, the use of additional fertiliser, shading against direct sunlight, a minimum temperature of 22⁰C during the day and 19⁰C during the night, a well defined resting period, and strict control of pests.

The plant must be kept in a well drained soil. If the soil becomes too dense (because of excess water or too much loam) the roots will rot. The health of a tuber is finally measured by its increase in size, and a tuber that is doing well may triple its weight in a single season.
 

Charles Shelton (on the left) and Marcelo Sellaro weighing the titan arum tuber
 

In cultivation at Kew, A. titanum shows a strong tendency to take dormant periods, usually twice during the growth cycle. When a leaf dies down after a regular growing season, the tuber will invariably take a rest period. Following this another leaf may emerge. When the plant is mature enough to flower, the resting period is usually considerably shorter and may take no longer than a month, or sometimes even less.

Rare flowerings of the titan arum

Pollination of different clones in cultivation rarely occurs. In 2009 two specimens flowered at Kew. This allowed cross-pollination using both fresh and frozen pollen grains, which were put on the stigmas on the first day of flowering. When the female flowers are receptive, the stigmas are very sticky and ready to receive pollen. The yellow rind of the appendix emits an overpowering, nauseating stench that gives the plant its Indonesian name of ‘bunga bangkai’, meaning “corpse flower”. The smell is perhaps the most powerful and disgusting odour produced by any plant. It was described by Sir Joseph Hooker (1891) as a mixture of rotting fish and burnt sugar, which turns your stomach over and makes your eyes run.

The stalk formed about 100 fresh berries, which turned into orange reddish fruits when ripe. After removal of the pulp the seeds were sown in a mixture of ½ part coir, ½ part sand, and watered daily. Seedlings were established after one month. Any seeds stored dry lose viability very quickly because the seed coat is rather thin and does not protect the embryo from desiccation (drying out).

Any success in propagating A. titanum, by any means, is a triumph of hope over adversity. For almost a century it was considered near impossible, but now the corner has been turned. Not only have viable seeds been produced in cultivation, but young plantlets have also been raised vegetatively by leaf cuttings.

If the features outlined in this text have captured your imagination, I hope that seeing a specimen growing in the Princess of Wales Conservatory will persuade you to explore the world of Aroids further, and serve as a general introduction to this impressive family of plants.

- Marcelo -
 

Find out more...

• More from Kew about the titan arum (Amorphophallus titanum)
• International Aroid Society
• Fairchild virtual herbarium
• Recommended reading – ‘Aroids: Plants of the Arum Family’ by Deni Brown

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