This species is closely related to Pachyrrhizus tuberosus, and sometimes treated as a subspecies of that species[, ].

Common Name: Yam Bean

General Information

Pachyrhizus erosus is a perennial climbing or trailing plant producing annual, twining stems 2 - 6 metres long from a tuberous rootstock[].
The plant is often cultivated for its edible root and seedpods in tropical areas[, ]. It also has a range of local medicinal applications and can be used as a pesticide. It is sometimes grown as a green manure.

Known Hazards

Whilst the roots are edible (and often eaten in quantity) the upper portions of the plant, especially the seeds, mature seedpods and the leaves, contain a poisonous glucoside[, , ]. This glucoside is more toxic to cold-blooded creatures than it is to mammals, and the pounded plant is sometimes dropped in water in order to stupefy fish[].
The mature seeds also contain a toxic resin[].

Botanical References

Range

Central America - northwestern Costa Rica to southern Mexico.

Habitat

Edges of deciduous forests and scrub vegetation; at elevations up to 1,750 metres but most commonly from 500- -900 metres.

Properties

Edibility Rating
Other Uses Rating
Habit	Perennial Climber
Height	6.00 m
Cultivation Status	Cultivated

Cultivation Details

Pachyrhizus erosus is tolerant of a wide range of climatic conditions but grows best in lowland tropical areas at elevations up to 1,000 metres and a moderate rainfall[, ]. The plant grows best in areas where the mean minimum temperature is about 20°c and the maximum is 30°c, though it can also succeed where they are 15 - 36°c[]. It is found in areas with a distinct dry season, where the mean annual rainfall is in the range 1,300 - 1,700mm, but can tolerate 250 - 7,000mm[].
Grows best in a sunny position[]. Tolerates a wide range of soils, being found in the wild on deep clays to sandy loams[]. Prefers a light, rich, well-drained, sandy soil[, ]. Dislikes water-logged soils[]. The plant prefers a pH in the range 6.5 - 8, but can tolerate 4.3 - 8[].
Immature pods are ready for harvest about 200 - 240 days from sowing[].
Tubers may be harvested after 150 - 270 days, before they become fibrous[]. In warmer parts of Mexico with light, rich soil, mature tubers are commonly harvested after only 90 days[].
Seed crops takes about 300 days to mature[].
A short-day plant, it requires between 11 - 13 hours of daylight hours per day in order to initiate tuber production[], though vegetative growth is normal even in relatively long days of 14 - 15 hours[].
When grown for its edible root the flowers and seedpods should be removed[, ].
There are some named forms[].
This species has a symbiotic relationship with certain soil bacteria, these bacteria form nodules on the roots and fix atmospheric nitrogen. Some of this nitrogen is utilized by the growing plant but some can also be used by other plants growing nearby[].

Edible Uses

Edible root - raw or cooked[]. Crisp, sweet and juicy, it tastes somewhat like an apple when raw and a water chestnut when cooked[, ]. The root stays crisp and does not discolour after being cut[]. It also stays crisp after being cooked, which makes it a popular substitute for water chestnuts in Chinese cooking[]. A starch extracted from the root is used in custards and puddings[].
The plant produces one or more turnip-shaped to elongated tubers up to 30cm in diameter and 25cm long. The root is usually harvested before it matures and becomes fibrous, when the plant has been growing for about 6 months and the tuber weighs about 2 kilos[]. Mature tubers can reach 2 metres long and weigh up to 20 kilos[].

Young seedpods - cooked and used as a vegetable[, , ]. They must be thoroughly cooked in order to destroy the poisonous principle rotenone[].

Medicinal

A decoction of the roots is used as a diuretic, and also in the treatment of fevers and haemorrhages[]

A warmed poultice of the stem pulp is applied to painful areas in the leg[].

The seeds are laxative. A tincture made from seeds is used in the treatment of herpes[].

The oil obtained from the seeds is purgative in doses of 40 gms[].

The seed is known to contain rotenoids, flavonoids and phenylfuranocoumarins which have been shown to have antifungal, antisecretory, antibacterial and spasmolytic activities. A study has shown CNS depressant effect with decreased locomotor activity, muscle relaxation, antianxiety and antiaggressive activity[].
Another study has shown moderate anti-herpes simplex virus activity[].

Agroforestry Uses:

The plant can be used as a green manure[].

Other Uses

The plant contains rotenone, the active ingredient in the insecticide 'derris', and it has the potential to be used as an insecticide[]. Derris is a relatively safe insecticide in that it does not affect warm-blooded animals and also breaks down into harmless substances with 24 hours of being used. It does, however, kill some beneficial insects and is also toxic to fish and amphibians[].

An extract of the root is used as an ingredient in commercial cosmetic preparations as a skin conditioner[]
An extract of the seed is used as an ingredient in commercial cosmetic preparations as a skin conditioner[].

The seeds yield around 38% of a colourless, limpid oil[]. No uses are given.

Propagation

Pre-soak the seed for 12 hours in warm water and then sow in situ[].
Division of the root tubers.
Cuttings.

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