Titan arum and relatives
"Our" titan arum (Amorphophallus titanum) has many relatives. There are about 200 species worldwide, all of them found in Africa or Asia. They belong to the arum family (Araceae). In the Bonn Botanic Gardens 34 species are in culture - very large and very small ones.
Titan arum
The titan arum (Amorphophallus titanum) was discovered in Sumatra in 1878 by the Florentine botanist Odoardo Beccari. It has the largest inflorescence in the plant kingdom.
Nowhere in Germany - probably even worldwide - there have been more flowering events than in Bonn. Therefore, it was obvious to choose the titanic inflorescence as the logo for the Botanic Gardens. The largest inflorescence to date - measured from the top of the tuber - was 3.25 m high.
A single pinnate leaf sprouts from the plant's underground tuber and dies after ten to fifteen months after providing the nutrients for the tuber's continuous growth. After the germination from the seed, the young plant takes several years until the tuber reaches a weight of about 20 kilograms, being large enough to sprout the first flower instead of the leaf. The inflorescence grows with great speed. A growth of up to 19.5 cm in twenty-four hours has been measured. The funnel-shaped bracts (spathe) shine like dark burgundy pleated velvet. From the spatha the bright yellowish cob (spadix) rises, the organ emitting odor and heat.
The titan arum's color, shape, and intense scent of carrion make it look like a large decomposing carcass to small nocturnal beetles, making it extremely attractive to them. They fall for the deception and crawl inside the flower to lay their eggs. In the process, they transfer the pollen and pollinate the plants.
The strong odor luring the insects is rhythmically emitted. The huge cob functions as a transmission mast and it can still be detected by insects at a distance of 22 kilometers. This is necessary, because titan arum plants are widely scattered in their natural habitat.
In the first flowering phase, the female flowers are ready for fertilization, and the plant attracts the hopefully pollen-laden insects with heavy bursts of scent.
In order to avoid self-fertilization, the plant enters the male phase and releases the pollen only afterwards. Therefore the scent emission is activated again.
After one to two days the flower closes again, and after three to four days the cob tips over. Eventually a more than one meter high fruit stand develops, bearing hundreds of bright orange-red berries. These berries are about five centimeters long, and will take eight months to ripen.
Relatives
The smallest one
The smallest of the genus is Amorphophallus ongsakulii. It was discovered only in 2004 in Laos. It reaches a height of about 5 cm, and the tuber has a diameter of 0.9 cm. For comparison, the tuber of the titanic arum which flowered this year weighed 80 kg!
The giant one
Amorphophallus gigas from Sumatra lives up to its name "gigas" - from the Greek: "huge". Its inflorescence stands on a stem, and if measured together they can reach a height of up to 5 meters. In Amorphophallus titanum the leaf and inflorescence are much larger.
The edible one
The elephant foot Amorphophallus paeonifolius has quite the bizarre inflorescence. Some varieties are edible and are grown as crops. The tubers, which weigh up to 9 kg, are eaten boiled or pickled as a vegetable or deep-fried like chips.