Dioscorea alata

• 1. Introduction

  ›

  Around 1939, a Mambatap greater yam grown in Maprik, in the East Sepik District of Papua New Guinea, reached 3.5 m in length. That giant root belonged to Dioscorea alata, a species of yam better known as ube. People also call it ubi, uwhi, purple yam or greater yam. Its tubers are usually a vivid violet-purple or bright lavender, though some are creamy-white or plain white. Its roots lie in the tropics of Asia and Oceania. This documentary asks how a single root collected so many names. It asks where the plant began and what carried it across open water. It also asks why a crop treasured at some tables is treated as a pest elsewhere.

  31222

• 2. A Root With Many Names

  ›

  The word ube comes from Tagalog, the language of the Philippines. The word uwhi comes from Māori, spoken in New Zealand. The two words are doublets, meaning each descends separately from one ancestor, the Proto-Austronesian word qubi.

  In English alone, the plant answers to ten-months yam, water yam, white yam, winged yam, violet yam and Guyana arrowroot. Sometimes it is called simply yam. Because it has become naturalized far from its origins, each region has coined labels of its own.

  Taro and a purple sweet potato from Okinawa, the variety 'Ayamurasaki', are often mistaken for it. Dioscorea alata is itself grown in Okinawa, which adds to the muddle. The shared ancestral word qubi points toward the seafaring Austronesian peoples, who are central to how this plant spread.

  582224

• 3. A Plant Made By People

  ›

  Scientists believe Dioscorea alata is a true cultigen, a plant known only in its cultivated forms. The vast majority of cultivars are sterile. That limits how the plant could have reached islands without human help, which makes it a good marker of human movement.

  Some authors have proposed an origin in Mainland Southeast Asia, but they offered no evidence. The greatest physical variation appears in the Philippines and New Guinea. For that reason the Philippines is named as the center of origin.

  This plant was not the only yam people took in hand. Several relatives were domesticated independently in Island Southeast Asia and New Guinea, and they set up a sharp contrast with the purple species.

  12121314

• 4. Safe Yams and Famine Yams

  ›

  The round yam, Dioscorea bulbifera, ubi gadung, Dioscorea hispida, and the Pacific yam, Dioscorea nummularia, were all tamed in the same region. So were the fiveleaf yam, Dioscorea pentaphylla, and the pencil yam, Dioscorea transversa. Most of these were treated as famine food. They carry higher levels of a toxin called dioscorine, so they must be prepared correctly before anyone eats them.

  Only two species were regularly cultivated and eaten, Dioscorea alata and the lesser yam, Dioscorea esculenta. Dioscorea alata was planted more widely than its partner. The reason was simple: its tubers grow much larger.

  That size and safety made both species ideal for a long trip by ship.

  12163435

• 5. Digging Up the Dates

  ›

  At the Kuk Swamp site in New Guinea, early farming plots and plant remains led some authors to a proposal. They suggest the yam was first domesticated in the New Guinea highlands from around 10,000 BP. They think it then spread into Island Southeast Asia with the Lapita culture at about 4,000 BP, together with Dioscorea nummularia and Dioscorea bulbifera. Dioscorea esculenta is believed to have gone the other way, brought into New Guinea by the Lapita. Contact with Austronesians also brought innovations to farming, including wet cultivation.

  Older clues complicate that story. Remains identified as probably Dioscorea alata turned up in the Niah Caves of Borneo, dated to the Late Pleistocene, before 40,000 BP. Others came from the Ille Cave of Palawan, at about 11,000 BP. Beside them lay remains of the toxic ubi gadung, which needs processing before it is edible.

  These finds do not prove cultivation. They do show that people already knew how to use starchy plants, and that the yam grew natively in Island Southeast Asia. They raise a lingering question: is it a true wild species, or a crop cultivated far longer ago than commonly thought?

  1617181921

• 6. Cargo on Austronesian Ships

  ›

  When Austronesian voyagers pushed across the sea, they packed their boats with plants. Dioscorea alata and Dioscorea esculenta were the most suitable for long transport. They traveled through all or most of the range of the Austronesian expansion. Dioscorea alata in particular was introduced to the Pacific Islands and New Zealand. Voyagers also carried it to Madagascar and the Comoros.

  In Southeast Asia the crop remains important, especially in the Philippines. In Melanesia it is also grown for ceremonial purposes tied to the size of the tubers at harvest time. In eastern Polynesia and New Zealand its role has faded. Other crops arrived there, most notably the sweet potato.

  In the Philippines, the purple variety found a second life in the kitchen.

  91011714

• 7. Purple on the Plate

  ›

  Ube tastes mildly sweet, earthy and nutty, something like sweet potato or taro. The violet cultivars contain a high amount of anthocyanins, pigments that turn a dish a distinctive vivid violet. The tubers are also valued for the starch that can be processed from them.

  In Philippine cuisine, where it is called ube or ubi, it goes into ube cake, ube cheesecake and ube crinkles. It also flavors ice cream, milk, donuts, tarts, jam and other pastries. It is often boiled or baked. It is also cooked into a sweetened dessert called ube halayá, a popular ingredient in the iced dessert halo-halo. More recently, these desserts have entered the United States through Philippine cuisine, under the Filipino name ube, and the striking color is a large part of the appeal.

  Purple varieties of sweet potato are easy to confuse with it, for they share color, taste and uses. Purple yam usually has a moister texture, and it carries more anthocyanin. Otherwise the two can be swapped in most recipes. The pigments dissolve in water, and they have been proposed as possible food coloring. Some gardeners also grow the plant for its looks.

  The same plant also turns up on supplement shelves, where the claims need a closer look.

  2224253637

• 8. Cautions and Claims

  ›

  Dioscorea alata is sold as a dietary supplement and used in folk medicine. There is no clinical evidence that it has any therapeutic properties. Supplements may cause adverse effects in people taking estrogens or anticoagulant drugs. They may also affect people who are pregnant or breast-feeding, and some people may have allergic reactions.

  The tuber itself has relatively high levels of oxalates, measured at 486-781 mg per 100 g of dry matter. Oxalates are linked to antinutritional effects and to the formation of kidney stones.

  Those are risks for people who eat the plant. In several countries the plant has also slipped out of human hands entirely.

  In the United States it persists in the wild in Hawaii, Louisiana, Georgia, Alabama, Puerto Rico and the U.S. Virgin Islands. It also persists in Haiti. Florida is the place where it is considered an invasive species.

  3335404142