Common Name: Devil's Tongue

General Information

Amorphophallus konjac is a perennial plant producing a single leaf each year that can be 100cm long, growing from a globose tuber that can be 30cm in diameter[]. It produces long, rhizomatous offsets that can be 50cm long and 3cm thick[].
This species is being increasingly cultivated for its edible tubers in Japan and China[, ]. It is grown as an ornamental in gardens and is said to make a good houseplant[].

Known Hazards

We have one report that this plant is very toxic raw, though no more details are given[]. It belongs to a family where most of the members contain calcium oxalate crystals. This substance is toxic fresh and, if eaten, makes the mouth, tongue and throat feel as if hundreds of small needles are digging in to them. However, calcium oxalate is easily broken down either by thoroughly cooking the plant or by fully drying it and, in either of these states, it is safe to eat the plant. People with a tendency to rheumatism, arthritis, gout, kidney stones and hyperacidity should take especial caution if including this plant in their diet[].

Botanical References

,

Range

E. Asia - southwest China.

Habitat

Loose leafy detritus in moist shady habitats[]. Forest margins and thickets at elevations of 830 - 1,200 metres in western Yunnan[].

Properties

Edibility Rating
Medicinal Rating
Other Uses Rating
Habit	Perennial
Height	0.75 m
Pollinators	Flies
Cultivation Status	Cultivated, Wild

Cultivation Details

Plants can tolerate a minimum temperature of 15°c during the growing season, though the optimum range is 20 - 25°c[]. The plants are not winter hardy outdoors in Britain but are sometimes grown outdoors in this country as part of a sub-tropical bedding display[].
The best crops are produced on deep, fertile, alluvial soils that are slightly acid[]. Dislikes heavy clay soils[]. Plants require some shade, especially when young[]. In the temperate zone it probably requires a position with at least moderate sun[]. Members of this genus generally require a moist but well-drained, humus-rich, fertile soil and a position in dappled shade[].
The plant produces one enormous leaf and one flowering stem annually. When ripe for pollination, the flowers have a foetid smell to attract carrion flies and midges. This smell disappears once the flower has been pollinated[].
The tuber is harvested in the autumn after top growth has been cut back by frost and it must be kept quite dry and frost-free over winter[, ]. It is then potted up in a warm greenhouse in spring ready to be planted out after the last expected frosts[].
The tubers are planted 15cm deep[].
Like many species in the family Araceae, this plant has the ability to heat the flowering spadix as the pollen becomes ready for fertilization. This heat greatly increases the strength of the aroma released by the plant, thus attracting more pollinating insects. It can also have the effect of making the insects more active, thus increasing the level of fertilization[].

Edible Uses

Corm - cooked[]. The root must be thoroughly boiled or baked, it is acrid when raw (see notes above on 'Known Hazards'[])[]. Very large, it can be up to 30cm in diameter[]. In Japan the large brown tubers are peeled, cooked and pounded to extract their starch, which is solidified with dissolved limestone into an edible gel called 'Konnyaku'[]. Konnyaku is a type of flour valued for its use in many dietary products[]. The flour is valued for its ability to clean the digestive tract without being a laxative[]. A nutritional analysis is available[]. This root is very high in water and low in calories, so it is being promoted as a diet food in N. America[].
Especially just before the foliage declines prior to dormancy, the tubers are a rich source of mannan, a polysaccharide of mannose and glucose[]. The mannose is extracted and widely used in foods for diabetics[]. Glucomannan, a soluble fibre formed from mannan and glucose, cannot be metabolized by the human body, but is metabolized by intestinal bacteria. Inside the digestive system, glucomannan absorbs up to 200 times its weight in water without any negative action upon the digestive system. It therefore can give a feeling of fullness and be of use to aid in weight loss, it also relieves constipation and irritable bowel syndrome, as well as reducing serum cholesterol levels[].
Glucomannan is widely used as an emulsifier and stabilizer in foods and drinks[].

Medicinal

The root is oxytocic and sialagogue[]. It is used in the treatment of cancer[].
Glucomannan, a soluble fibre obtained from the tuber, cannot be metabolized by the human body, but is metabolized by intestinal bacteria. Inside the digestive system, glucomannan absorbs up to 200 times its weight in water without any negative action upon the digestive system. It therefore can give a feeling of fullness and be of use to aid in weight loss, it also relieves constipation and irritable bowel syndrome, as well as reducing serum cholesterol levels[].

The flowers are febrifuge[].

Agroforestry Uses:

A system of cultivation, known as jinjenjo, is often practised in Japan. In this, the plants are grown in a natural plant community and are heavily mulchd with grain straw or wild herbs. The plants thus grown are remarkably free from pests and diseases. The largest tubers are harvested at the end of the year, leaving the rest in the ground to grow on for harvest in later years[].

Other Uses

The plant has insecticidal properties[].

Glucomannan, obtained from the tuber, has a wide range of used in various industries. It has gelling and film-forming properties and is widely used as an emulsifier and stabilizer in foods, drinks, cosmetics and the pharmaceutical industry. It is also used as a non-clay drilling fluid in the diamond and oil industries[].

Propagation

Seed - best sown in a pot in a warm greenhouse as soon as it is ripe and the pot sealed in a plastic bag to retain moisture. It usually germinates in 1 - 8 months at 24°c[]. When large enough to handle, prick the seedlings out into individual pots and grow them on in the greenhouse for at least a couple of years. Plant them out in late spring or early summer, after the last expected frosts, and give them some protection such as a cloche until they are growing away strongly.
Division of offsets[]. These are rarely produced[].