A stinky plant that produces heat? The strange case of Amorphophallus titanum

It is one of the most peculiar plants in the world. For example, it has the largest known unbranched inflorescence in the plant kingdom. Discovered in 1878 by the Italian naturalist Odoardo Beccari, it is popularly known as titan arum or “bunga bangkai”. The latter term, meaning “corpse flower”, is Indonesian, which gives us some clue as to its origin: the lush jungles of Borneo and Indonesia. Its scientific name, Amorphophallus titanum, means titanic amorphous phallus.

The plant flowers only 3 or 4 times during its life and for a very short time, since the flower remains alive for only 3 days. This is why botanical gardens that have a specimen become a hive of visitors when the time of flowering arrives. Actually, it is not correct to speak of a “flower”, but rather of an inflorescence, that is, a structure in which multiple flowers are arranged with a specific organization.

The plant sprouts from a tuber. It starts with a single, huge, modified leaf, the spathe, and a stem. From this grows a spike-like inflorescence called spadix (similar to that of cattail, for example), where the true flowers are arranged, which are male (arranged at the top) and female (located at the bottom). This organ gives off a foul odor of rotting flesh that attracts pollinating insects, which is also the origin of its popular name.

The inflorescence grows at a rate of 10 cm per day and can reach a height of 3 meters, a meter in diameter and a weight of 75 kg, although in 2003 the German University of Bonn presented a specimen weighing 126 kg!

The flowering process can be divided into two phases: the first occurs during the first afternoon and evening after the opening of the leaf or spathe and involves the flowering of the female flowers. The second phase occurs the following night, when the male flowers bloom.

As if its peculiarities were not enough, it has also been observed that it emits heat. This phenomenon, known as thermogenesis, was recorded in 2006 during the flowering of a corpse flower specimen, whose spadix reached a temperature of 36-38°C!

Thermogenesis is the ability of some organisms to produce heat through internal metabolic processes. The family to which the corpse flower belongs (Araceae) also includes other species with thermogenic capacity, some even raising their temperature up to 12ºC above the ambient temperature.

There are several hypotheses about the origin and evolution of this process, which is closely linked to the flowering phases. One of the most widely accepted assures that it favors pollination by insects. These are attracted by the rotting aromas emitted by the plant and originating from the evaporation of volatile compounds. The increase in temperature during thermogenesis enhances this process.

Normally, the female sex organs mature before the male flowers release pollen in plants with thermogenic capacity. Moreover, it is during the female phase when the greatest amount of heat is produced and, therefore, when the plant is most likely to be visited by pollinating insects. This strategy is very useful, as the plant ensures that it is pollinated with pollen from a different individual and avoids pollination with its own pollen.

On the other hand, insects do not leave empty-handed. It is thought that the heat generated during thermogenesis serves as a reward for pollinators, so that a mutualistic relationship is established between both parties. Insects are ectothermic animals, i.e. their body temperature depends on that of the environment. The execution of their vital activities (movement, copulation, etc.) requires the energy generated by metabolic processes, for which a high body temperature is required. Thus, the corpse flower would act as a recharging station where insects can warm up to continue their tasks.