| Dioscorea alata | |
|---|---|
 | |
| Cross section of purple yam | |
Scientific classification | |
| Kingdom: | Plantae |
| Clade: | Tracheophytes |
| Clade: | Angiosperms |
| Clade: | Monocots |
| Order: | Dioscoreales |
| Family: | Dioscoreaceae |
| Genus: | Dioscorea |
| Species: | D. alata |
| Binomial name | |
| Dioscorea alata | |
| Synonyms[2] | |
List
| |
Dioscorea alata – also calledube (/ˈuːbɛ,-beɪ/),ubi,purple yam, orgreater yam, among many other names – is a species ofyam (atuber). The tubers are usually a vividviolet-purple to brightlavender (hence the common name), but some range from creamy-white to plain white. It is sometimes confused withtaro and the Okinawa sweet potatobeniimo (紅芋) (Ipomoea batatas 'Ayamurasaki'), howeverD. alata is also grown in Okinawa. Its origins are in the Asian and Oceaniantropics.[3] Some varieties attain to great size. A "Mambatap" greater yam grown in Maprik, East Sepik District, Papua New Guinea around 1939 was 3.5 m (11 ft) in length.[4][5]
Because it has become naturalized following its origins in Asia, specifically thePhilippines, through tropical South America, and the southeastern United States,D. alata is referred to by many different names in these regions. In English alone, aside from purple yam, other common names includeten-months yam,water yam,white yam,winged yam,violet yam,Guyana arrowroot, or simplyyam.[3]
 | This articleis missing information about wild relatives (D. nummularia, D. transverse, and D. hastifolia; progenitor unknown) [doi:10.1111/boj.12374]). Please expand the article to include this information. Further details may exist on thetalk page.(October 2021) |
Dioscorea alata is one of the most important staple crops inAustronesian cultures. It is one of various species of yams that were domesticated and cultivated independently withinIsland Southeast Asia andNew Guinea for their starchytubers, including the round yam (Dioscorea bulbifera),ubi gadung (Dioscorea hispida), lesser yam (Dioscorea esculenta), Pacific yam (Dioscorea nummularia), fiveleaf yam (Dioscorea pentaphylla), and pencil yam (Dioscorea transversa).[6] Among these,D. alata andD. esculenta were the only ones regularly cultivated and eaten, while the rest were usually considered asfamine food due to their higher levels of the toxindioscorine which requires that they be prepared correctly before consumption.[7]D. alata is also cultivated more thanD. esculenta, largely because of its much larger tubers.[8]
D. alata andD. esculenta were the most suitable for long transport in Austronesian ships and were carried through all or most of the range of theAustronesian expansion.D. alata in particular were introduced into thePacific Islands andNew Zealand. They were also carried byAustronesian voyagers intoMadagascar and theComoros.[9][10][11]
The center of origin of purple yam is inthe Philippines, but archaeological evidence suggests that it was exploited inIsland Southeast Asia andNew Guinea before theAustronesian expansion. Purple yam is believed to be a truecultigen, only known from its cultivated forms. The vast majority of cultivars are sterile, which restricts its introduction into islands purely by human agency, making them a good indicator of human movement. Some authors have proposed, without evidence, an origin inMainland Southeast Asia, but it shows the greatest phenotypic variability in thePhilippines andNew Guinea.[12][13][14]
Based on archaeological evidence of early farming plots and plant remains in theKuk Swamp site, authors have suggested that it was first domesticated in the highlands of New Guinea from around 10,000BP and spread into Island Southeast Asia via theLapita culture at around c. 4,000BP, along withD. nummularia andD. bulbifera. In turn,D. esculenta is believed to have been introduced by the Lapita culture into New Guinea. There is also evidence of an agricultural revolution during this period brought by innovations from contact with Austronesians, including the development ofwet cultivation.[15][16]
However, much older remains identified as being probablyD. alata have also been recovered from theNiah Caves ofBorneo (Late Pleistocene, <40,000BP) and theIlle Cave ofPalawan (c. 11,000BP), along with remains of the toxicubi gadung (D. hispida) which requires processing before it can be edible. Although it doesn't prove cultivation, it does show that humans already had the knowledge to exploit starchy plants and thatD. alata were native to Island Southeast Asia. Furthermore, it opens the question on whetherD. alata is a true species or cultivated much older than believed.[6][17][18][19][20][21]
Purple yam remains an important crop in Southeast Asia, particularly in thePhilippines where the vividly purple variety is widely used in various traditional and modern desserts. It also remains important inMelanesia, where it is also grown for ceremonial purposes tied to the size of the tubers at harvest time. Its importance in easternPolynesia andNew Zealand, however, has waned after the introduction of other crops, most notably thesweet potato.[8]
Purple yams have edible tubers which have a mildly sweet, earthy and nutty taste, reminiscent ofsweet potatoes ortaro. The violet cultivars, in particular, turn dishes distinctively vivid violet because of the high amount ofanthocyanins.[22] Purple yams are also valued for thestarch that can be processed from them.[3] Purple yam is most common inPhilippine cuisine (where it is known asube orubi). It is widely applied for many Philippine desserts, such asube cake,ube cheesecake andube crinkles, as well as an ingredient or flavor forice cream,milk,donuts,tarts, jam and other types ofpastries. It is often eaten boiled, baked, or as a sweetened dessert calledube halayá; the latter being a popular ingredient in the iced dessert calledhalo-halo.[23][24][25] Purple yam desserts have more recently entered theUnited States through Philippine cuisine, under the Filipino name "ube". It is particularly popular due to the striking violet-purple color it gives to desserts.[22][23][26]
Purple yam is commonly confused with purple/violet varieties ofsweet potatoes because of their similarities in color, taste, and culinary uses. However, like other yams, purple yam tends to have a moister texture than sweet potatoes. Purple yams also have higher anthocyanin content than sweet potatoes. They can otherwise be used interchangeably in most recipes.[27][28]
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Although available as adietary supplement and used infolk medicine, there is noclinical evidence thatD. alata has any therapeutic properties.[29] Use ofD. alata supplements may haveadverse effects in people takingestrogens,anticoagulant drugs or during pregnancy and breast-feeding.[29] Some people may haveallergic reactions to use ofD. alata supplements.[29]
D. alata has relatively high levels ofoxalates (486–781 mg/100 g dry matter),[30] which are associated withantinutritional effects andkidney stone formation.[31]
The color of purple varieties is due to variousanthocyanin pigments.[32] The pigments are water-soluble, and have been proposed as possiblefood coloring agents.[33]D. alata is sometimes grown in gardens for its ornamental value.[3]
Dioscorea alata is native to the Philippines, as well as surrounding areas (Taiwan and theRyukyu Islands ofJapan). It has escaped from its native growth area and into the wild in many other places, becomingnaturalized in parts of southern and east-centralChina,Africa andMadagascar, theWestern Hemisphere, and various islands in theIndian andPacific oceans.[34][35] It persists in the wild in Haiti, as well as theUnited States, inHawaii,Louisiana,Georgia,Alabama,Puerto Rico, theU.S. Virgin Islands, and inFlorida where it is considered aninvasive species.[36][37]
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