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.
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.
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.
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.
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.
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
Light: full sun summer, shade in winter
Soil: 80 % peat
Water: water only when growing, dry when dormant
USDA Hardiness Zone: tropical