The root is edible - not the rest of the plant!
Pachyrhizus is a small genus of five or six species of tropical and subtropical plants growing from large, often edible taproots.
The root of the Yam bean (Jicama) is edible with a crisp and crunchy texture. It is called Mexican turnip or Mexican potato. Ideal if planted in August and September. Tubers development begins at flowering as days begin to shorten and days get cooler. Harvest in 5-6 months. Roots weigh 1.5 -3 pounds.
It is a vine
The yam bean (Pachyrhizus spp) is a legume but unlike its close relatives the soybean and other beans, the yam bean is cultivated for its large, tuberous roots. Long vines can grow twenty feet long and produce delicious tubers. It is usually consumed fresh, cut in strips in salads or marinated in lime or dried and ground into flour for use in cakes and desserts.
Caution: The seeds and pods are poisonous! The pods are toxic when mature. In contrast to the root, the remainder of the jícama plant is very poisonous; the seeds contain the toxin rotenone, which is used to poison insects and fish.
The plant is a climbing vine with flat, kidney-shaped seeds, and the tubers range in weight from 0.5 to 2.5 kg. Its white/blue flowers are often removed (a process known as reproductive pruning) to increase yield and biomass of the tubers.
The jícama vine can reach a height of 4–5 m given suitable support. Its root can attain lengths of up to 2 m and weigh up to 20 kg. Jicama is frost-tender and requires 9 months without frost for a good harvest of large tubers.
Root can be eaten raw
The root's exterior is yellow and papery, while its inside is creamy white with a crisp texture that resembles raw potato or pear. The flavor is sweet and starchy, reminiscent of some apples or raw green beans, and it is usually eaten raw, sometimes with salt, lemon, or lime juice and chili powder. It is also cooked in soups and stir-fried dishes.
The seeds are available from the University of Hawaii Seed Lab: http://www.ctahr.hawaii.edu/seed/seeds.asp
How to grow Jicama the Mexican Yam Bean, Pachyrhisus erosus, in Hawaii:
Yam bean - FAO http://buff.ly/2jcAmHx
Jicama or Yam Bean seeds | Baker Creek Heirloom Seeds http://buff.ly/2ipjboS
Pachyrhizus erosus - Wikipedia http://buff.ly/2jcvdz8