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Worlds Largest, Smelliest Flower – Titan Arum

 The titan arum (Amorphophalus titanum) is reported to be the worlds largest flower but this is not strictly true. It is however one of the most interesting plants.

Amorphophallus titanum - titan arum

Amorphophallus titanum – titan arum: by Robert Pavlis

What is a Flower?

A flower is defined as the part of a plant that makes seed. The Titan arum has many such parts inside the structure that we think of as being the flower. The large structure that we see is more correctly called a ‘flowering structure’ or ‘inflorescence’ and it contains many small flowers. The Titan arum is also not the largest flowering structure in the world. The talipot palm, Corypha umbraculifera is larger, but it is a branched inflorescence. What we can correctly say about A. titanum is that it is the largest unbranched inflorescence in the world.

This is not a plant for your garden, but it is a very fascinating plant. It originates in the rainforests of Sumatra and is now grown at many of the larger botanical gardens. I recently had a chance to see it in flower at the University of Guelph which has 4 mature plants. The first plant to flower in Guelph was grown from seed by Rodger Tschanz and took 11 years to flower.

Amorphophallus titanum - titan arum

Amorphophallus titanum – titan arum by Robert Pavlis

The name Amorphophalus titanum translates loosely to “giant misshapen penis”. It’s common names include titan arum and corpse flower.

The plant is a tuber (or corm – the experts don’t agree) that is dormant for part of the year. In a blooming year, it will first send up a single spike which eventually becomes the flowering structure. This then dies away, and is followed by a single leaf which can be 6 meters (20 ft) tall and 5 meters (16 ft) across. The flowering structure has the typical arum look with a green/reddish spathe and a tan coloured spadix coming out of the center. The inside of the spadix looks like a stick of french bread. The flowering structure can be 9 feet tall and 3 feet wide. The real flowers are relatively small and are located at the bottom of the spadix.

Amorphophallus titanum - titan arum

Amorphophalus titanum, male flowers in center, female below

In the wild the plant flowers about every 3 – 8 years with the male flowers opening a day after the female flowers to ensure that cross-pollination takes place. To make this happen the plant needs to attract pollinators from a long distance away, and it has a special way to accomplish this. Firstly, it sends out a very strong foul-smelling sent that attracts flies and some bees. Secondly, it heats up the spadix to vaporize the odours which makes them even more powerful.

The heat generated by the spadix (thermogenesis) is what makes this plant so interesting. for the plant pictured above we measured the temperature at 3:00 pm on the day these pictures were taken. The bottom of the plant was 24 C and the top of the spadix was 39 C. How does a plant produce such a large amount of heat? Scientists are still trying to understand this, but it seems that other arums use a chemical reaction that is similar to the one animals use to generate body heat. You could say that the arums are ‘warm blooded’ – not a completely true statement, but a close analogy.

The heating of the spadix puts great energy demands on the plant and so it should be no surprise that the plant controls the heating process to gain maximum benefits from the process. Firstly, it does not heat the whole spadix – it only heats the tip – the part that is highest in the air. Remember it is all about dispersing the scent as far as possible.

Thermogenesis in the Titan Arum

The diagram below shows the sequence of events. During the first night the female flowers are ready to accept pollen, and the tip of the spadix is heated to high temperatures to maximize the attraction of insects. Heating takes place for a short period of time to conserve energy. Presumably it also happens when the insects are active – during the night. Insects stay in the flower during the next day – possibly for mating. On the second night, the spadix does not heat up which means that there is much less smell produced. The part of the flower containing the male flowers does heat up, indicated by the dashed line in the diagram. The reason for heating the male flowers is still not understood, but it may help the resident insects become more active so that they visit another flowering plant.

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ref:  Plant Signal Behav. 2009 November; 4(11): 1096–1098, original article

You might think that such weird plants only grow in the tropics – you’d be wrong. Our eastern skunk cabbage is an arum and also uses thermogenesis.

The plant seems to be fairly easy to grow in a greenhouse if you have the patience and space.

General Information:

Name Pronunciation:  ah-MOR-foe-phal-us ti-TAN-um

Life Cycle: perennial

Height: 6 meters (20 ft)

Bloom Time: any time

Natural Range: Sumatra

Habitat: rainforests, steep hills

Synonyms: none

Cultivation:

Light: full sun summer, shade in winter

Soil: 80 % peat

Water: water only when growing, dry when dormant

USDA Hardiness Zone: tropical

Propagation: seeds

References:

1) Photo Source for Amorphophalus titanum, male flowers in center, female below, source is Wikipedia

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Robert Pavlis
Editor of GardenMyths.com
I live in southern Ontario, Canada, zone 5 and have been gardening a long time. Besides writing and speaking about gardening, I own and operate a 6 acre private garden called Aspen Grove Gardens which now has over 3,000 perennials, grasses, shrubs and trees. Yes--I am a plantaholic!

I hope you find Garden Myths an educational site that helps you understand your garden better.

4 Responses to 'Worlds Largest, Smelliest Flower – Titan Arum'

  1. ginny says:

    Robert, I have a plant, or I should say an invasion or plants, that look very similar to this plant. The difference is that it starts with leaves and grows and finally a purple like flower appears with a center “penis” like spike, and it stinks. The purple flower part has a “bulb” like cup at the bottom and then becomes larger and spreads out and is very smooth, no pleats, and then the spike is in the center, from the bottom. I tried to get rid of it and only made it spread, yikes! My Great-Aunt, she would be 115 now, was a “plant pirate” and used to bring plants back from where ever she had been traveling so I have no idea where it came from. I thought I had some pictures of it but am not able to find them. She, my grt-aunt, never traveled to any foreign countries, only Canada, and only by car. I really can’t imagine someone wanting this plant in their yard and I never noticed it before until I started digging up this part of garden and then it just “exploded”. We have had a mild winter here in Portland, Oregon and I have already been outside gardening and noticed that the plant is sending up it’s leaves and there are so many that it is invading my Lavender plants.

  2. Inger Knudsen says:

    Great entry very interesting to read the explanation

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  1. […] heats up the spadix to vaporize the odours and send them even further away. For example, in one experiment, the temperature of the plant was measured to be 24C (75F), and the temperature of the spadix was a […]

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