Pachyrhizus is a small genus of flowering herbs and subshrubs in the legume family Fabaceae, order Fabales. It comprises five or so species native to the tropical and subtropical Americas, with a range stretching from northern Mexico south to northwestern Argentina. The genus is perhaps best known as the source of jícama (P. erosus), one of the most widely consumed root vegetables in Central America and Asia.
Plants in the genus are characterized by large, starchy taproots that are often edible, along with twining or erect stems bearing trifoliate leaves and clusters of white to lilac flowers typical of the legume family. They favor seasonally-dry tropical habitats — forest margins, scrub vegetation, and open grassy areas — and several species also thrive in humid Amazonian conditions.
Beyond jícama, the genus includes Pachyrhizus tuberosus (Amazonian yam bean), an annual vine cultivated by indigenous peoples of the Amazon basin for its protein-rich tubers and edible leaves, and Pachyrhizus ahipa (ahipa or Andean yam bean), a non-climbing species adapted to high-altitude Andean conditions up to 2,000 m elevation. All three of these species have edible roots, though it is worth noting that other parts of the plants — particularly the mature seeds of P. erosus — contain rotenone, a toxic compound historically used as an insecticide.
Etymology
The genus name Pachyrhizus derives from the Greek words pachys (thick) and rhiza (root), a direct reference to the characteristically large, swollen taproots that distinguish these plants. The name was established by L.C. Richard and Augustin Pyramus de Candolle.
Distribution
Pachyrhizus species are native to the tropical and subtropical Americas, with the genus's natural range extending from northern Mexico through Central America and into South America as far south as northwestern Argentina. Pachyrhizus erosus has been introduced and is now widely cultivated across Southeast and East Asia — including China, Malaysia, Indonesia, the Philippines, and Thailand — where it is an important market vegetable.
Ecology
The genus occupies seasonally-dry tropical forests and thickets, often colonizing forest margins, scrub vegetation, and open grassy areas. Pachyrhizus tuberosus is an exception, thriving in the acid soils of South America's tropical rainforests. Like all legumes, Pachyrhizus species fix atmospheric nitrogen through root symbioses, contributing to soil fertility in the agroecosystems where they are grown.
Cultivation
Jícama (P. erosus) is the most widely cultivated species and is grown commercially throughout Central America, Mexico, and large parts of Asia. P. tuberosus is cultivated by Amazonian indigenous communities, valued for its high-protein (up to 32%) seeds and edible leaves. P. ahipa is a subsistence and local-market crop in Bolivia and the high Andes, and was introduced to the West Indies by British scientists in the 19th century. Cultivation typically favors warm, seasonally-dry climates with well-drained soils; P. tuberosus tolerates wetter, more acidic conditions.
Cultural Uses
All three major Pachyrhizus crops have been cultivated by indigenous peoples of the Americas for centuries. The jícama root is a staple snack food in Mexico and Central America, eaten raw with lime and chili, and features in Asian stir-fries and salads under regional names including sengkuang (Malaysia), bengkoang (Indonesia), singkamas (Philippines), and mankew (Thailand). The seeds of young plants are sometimes eaten like lima beans in regions where jícama is native, but mature seeds are toxic due to high rotenone content and have been used as an insecticide.
