21 December 2010
Second year apprentice, Scarlett English writes about the genus Amorphophallus and a new display in the Princess of Wales Conservatory.
The titan arum
All that most people know of the tropical tuberous genus of Amorphophallus is the heroically nasty odour of the Sumatran Giant, the titan arum (Amorphophallus titanum). While some species of Amorphophallus are fragrant with aromas of citrus, fruit, anise and chocolate, and many growing in zone 8 in the tropical nursery don't seem to smell at all, the titan arum emits a nauseating odour of rotten meat. It boasts one of the largest and smelliest inflorescences in the world, but why is it so smelly (and what is an inflorescence)?
The answers lie in the morphology, or the flower forms of the genus. Amorphophallus flowers are very small, but grouped in large flowering structures called inflorescences. The inflorescence of every Amorphophallus species and every plant in the family of Araceae, consists of a bract (modified leaf) called a spathe, surrounding a spike-shaped organ called a spadix.
Amorphophallus species have unisex male and female flowers are found in bands at the base of the spadix. They are pollinated by flies or beetles and to attract them the inflorescence emits an alluring odour which can be pleasant or revolting to humans. Parts of the spadix also warm up to help intensify and push the odour farther – it might also act as an infrared attractant for pollinators as well.
While I’ve been working in tropical nursery, the Amorphophallus konjac has flowered – phew, it smells like a dead rat behind a radiator. And as if the smell wasn't enough, the purple-red flowers with green blotches even look like rotten meat, enticing their pollinators by mimicking their favourite dish. This is not uncommon among some of the stinkier species. And some species, such as A. cirrifer, even have hairs on the flowers so as to look like hairy dead animals.
Luckily, the flowers are not the only thing that’s interesting about these extraordinary plants, even if you do have to hold your nose to get close. These plants are seasonally dormant or 'geophytic'. Tuber size varies hugely from species to species, with some the size of a small marble (A. polyanthus) and others weighing up to 75kg (A. titanum).
Each one sends up a single leaf every growing season, which is long stalked and so deeply divided and lobed that it looks more like a sapling or a small tropical tree. The leaf stalk of the A. titanum can reach up five metres with a diameter of up to 30cm. The leaf blade grows to a width of up to four metres. When mature, the tuber will send up a single inflorescence instead of a leaf. Although some species don't stick to the rules, such as A. variabilis, which can send up numerous flowers and leaves at the same time.
Amorphaphallus display in the Princess of Wales Conservatory
I find just about every part of the anatomy of Amorphophallus species utterly astonishing, and every day I spend working with them I learn more incredible truths about this beautiful but monstrous genus. In the Princess of Wales Conservatory there is currently an Amorphaphallus display, showcasing a number of species in flower or in leaf. This includes a specimen of Amorphophallus titanum which is in leaf at the moment, but there are many plants in the nursery that will in the future come into flower, so watch this space.
Frequently Asked Questions
What plant family is this genus in?
The Araceae family, commonly known as the Aroid family. This also includes Arums, Anthuriums and the Swiss cheese plant.
How many species are in the Genus?
Where do they grow naturally?
The Paleotropics, a region stretching from West Africa eastwards into Polynesia. They grow in tropical humid forests, seasonally dry forests with wet periods and open woodlands.
How do they reproduce?
By seed and by production of tubercles, tuberous offsets from the main tuber.
How do we grow them at Kew?
In moist, humus-rich compost in warm temperatures around 22 degrees Celsius in about 75% humidity.
Where can you find them?
In the Princess of Wales Conservatory or - on a Tropical Nursery Open Day - in zone 8 in the Tropical Nursery.