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At the moment, a specimen of Amorphophallus titanum, the Titan Arum, also known as the Giant penis plant, is flowering in the Tropical Glasshouses for the second time this year. The flowering can also be followed via a live stream on the Hortus' YouTube channel. On 14 July there was also a Titan Arum in bloom in the Hortus. It is exceptional that two specimens of this plant bloom so soon after each other.

Those who missed the previous one will therefore get a second chance. The inflorescence of Amorphophallus titanum is short but powerful: after about 48 hours, the inflorescence collapses. The flowering of the Titan Arum is unique because of its large size and intense smell. When the plant flowers, it spreads a stench reminiscent of rotting meat that can be smelled from hundreds of metres away.

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Thermal camera
During this flowering, a thermal camera is also set up near the plant. This camera makes visible what you cannot see with the naked eye: the spadix of the plant warms up when it flowers. Why does it do this? The combination of the smell and the heat is ideal for attracting scavenging insects from far and wide. Flies and beetles are attracted by the smell and crawl into the spathe, looking for a tasty snack. Of course, there is none, but the purpose of the plant has been achieved: pollination.

By measuring the heat, we can see exactly when the plant flowers. Only during flowering does the green-yellow spadix warm up to about 38 degrees. So we not only know exactly when and for how long the plant flowers, but also when it has finished flowering. You can see how warm the spadix is on our livestream.

Short flowering period
Flowering is short, only two days. Why so short? It is part of the strategy of this plant. It faces two challenges: flowering costs a great deal of energy and it cannot pollinate itself. This means that it cannot fertilise female flowers with its own male pollen. This is to prevent inbreeding.

That is why the plant flowers female the first day. The female flowers at the bottom of the spadix open and the cob spreads a penetrating stench of rotting flesh that can be smelled hundreds of metres away. The combination of the smell and the warm spadix attracts flies and beetles, which sit in the spathe on the female flowers. After a day, the female flowers stop blooming and the male flowers open. These bloom odourlessly and are covered in pollen. The flies and beetles realise that the inflorescence is not a tasty snack after all and fly out of the spathe, past the male flowers, and become covered in pollen. After this great effort, the plant runs out of energy and collapses.

Then comes a crucial moment: somewhere in the vicinity, another Giant Arum flowers (this can be kilometres away). This inflorescence also spreads a stench and attracts all the flies and beetles in the vicinity, including those that visited the aforementioned inflorescence. They land on the female flowers of the next specimen and pollinate the flowers with the pollen of the previous one. Only when this happens, the pollination is complete.

How is it possible that so many Titan Arums have bloomed recently?
Flowering Titan Arums are rare, we always say. Yet this is the third one to flower in one year. How is that possible? One explanation for why so many specimens bloom so soon after each other is the renovation of the Tropical Glasshouses in 2013. The conditions of the glasshouse were so variable in that period that the collection suffered a major blow. This is because the plant demands high humidity and a constant heat of at least 24°C. They needed a long time to recover. The growth cycle was 'reset', as it were. Amorphophallus planys, which get their energy from a tuber under the ground, need about ten years to store enough energy to flower. Those ten years have just about passed, so it is now time for many of them to start flowering. 

In addition, for a number of years we have been receiving help in caring for our penis plant collection from volunteer Rudmer Postma. Rudmer is a true Amorphophallus enthusiast and takes good care of the collection, from timely repotting to giving special fertiliser mixtures.

Fact sheet
Latin name: Amorphophallus titanum
Common names: penis plant, giant penis plant, giant arum, Sumatran arum
Country of origin: Indonesia, Sumatra
Family: Arum family (Araceae)
IUCN status: Endangered
Largest unbranched inflorescence of any known plant

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