Common Name: Elephant Yam

General Information

Elephant yam is a herbaceous, perennial plant producing either one or two large leaves annually that can be up to 2 metres tall. These leaves grow from a massive underground tuber that can weigh up to 25 kilos[].
The plant is cultivated for its edible tuber in lowland tropical Asia[, ]. It is an important stand-by crop in many regions, especially in years when the rice crop fails[].

Known Hazards

The tuber of the wild species is considered to be totally toxic and inedible, the wild plant only being used for medicineal purposes[].
Although no specific mention has been seen for the cultivated forms of species, 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 - China, Indian subcontinent, Myanmar, Thailand, Laos, Vietnam, Malaysia, Indonesia, Philippines, New Guinea, north Australia, western Pacific

Habitat

Loose leafy detritus in moist shady habitats[]. Tropical conditions in secondary forests, shrub forests and grasslands in arid valley areas at elevations below 750 metres[].

Properties

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

Cultivation Details

A temperature in the range of 25 - 35°c is required with an annual rainfall of 1,000 - 1,500mm[]. Corm development is promoted during dry periods[]. Cultivated for its edible tuber in Asia, plants are not winter hardy outdoors in the temperate zone, but are sometimes grown as part of a sub-tropical bedding display in temperate areas with a long, warm, frost-free season[].
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 tropics, but grow better in a sunny position in temperate areas[]. Members of this genus generally require a moist but well-drained, humus-rich, fertile soil and a position in dappled shade[].
The plants are usually grown on a three year cycle in the tropics[]. An interesting technique used in Indonesia is to dig up the tuber after one year and then replant it upside down. This stimulates the lateral buds into growth and increases the overall size of the tuber[].
In temperate zones 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 about 15cm deep after the last expected frosts.
Yields of 20 tonnes per hectare can be achieved[].
There are many cultivated forms, some of which have a lower content of calcium oxalate crystals and less or no alkaloids[].
The plant produces one or two enormous leaves and one short flowering stem annually. When ripe for pollination, the flowers have a foetid smell to attract carrion flies and midges. This smell disappears once the flowers have been pollinated[].
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[, , , ]. Acrid raw[], it must be thoroughly boiled or baked (see notes above on 'Known Hazards'[])[, ]. A very large root, it can be up to 50cm in diameter[, , ]. Corms are usually harvested when three years old, at this stage they can weigh up to 9kg[]. The corms can be stored for several months at 10°c[]. Some caution is advised, see notes above on toxicity. The fresh corms are turned into curd, or are chopped then dried[]. The curd is relatively tasteless, but it absorbs flavours well and so can be used as a carbohydrate element in a wide range of other foods[].

Young leaves and petioles - cooked and used as a vegetable[]. They must be thoroughly cooked[, ]. Caution is advised, see notes above on possible toxicity.

Medicinal

The root is carminative, restorative, stomachic and tonic[, ]. It is dried and used in the treatment of piles and dysentery[, , ]. The fresh root acts as an acrid stimulant and expectorant, it is much used in India in the treatment of acute rheumatism[, ]. Some caution is advised, see the notes above on toxicity.

The stem is cut, and the inside of the stem eaten raw, in the treatment of snakebites[].
The sap from the petiole is fermented and drunk as a treatment for diarrhoea and dysentery[].

Agroforestry Uses:

Plants are often grown as an understorey crop in woodlands or in plantations of betel (Areca spp.), coconuts (Cocos nucifera), bananas (Musa spp.) or coffee (Coffea spp.)[].

Other Uses

None known

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.