Dioscorea alata

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-purpleto brightlavenderin color (hence the common name), but some range in color from cream to plain white. It is sometimes confused withtaroand the Okinawa sweet potatobeniimo(紅芋)(Ipomoea batatascv.Ayamurasaki), howeverD. alatais also grown in Okinawa. With its origins in the Asian and Oceaniantropics,D. alatahas been known to humans since ancient times.
Because it has become naturalized following its origins in Asia, specifically thePhilippines, through tropical South America, and the southeastern U.S.,D. alatais 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.
Dioscorea alatais 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 AsiaandNew Guineafor their starchytubers, including the round yam (Dioscorea bulbifera), ubi gadong (Dioscorea hispida), lesser yam (Dioscorea esculenta), Pacific yam (Dioscorea nummularia), fiveleaf yam (Dioscorea pentaphylla), and pencil yam (Dioscorea transversa).Among these,D. alataandD. esculentawere the only ones regularly cultivated and eaten, while the rest were usually considered asfamine fooddue to their higher levels of the toxindioscorinewhich requires that they be prepared correctly before consumption.D. alatais also cultivated more thanD. esculenta, largely because of its much larger tubers.
D. alataandD. esculentawere the most suitable for long transport in Austronesian ships and were carried through all or most of the range of theAustronesian expansion.D. alatain particular were introduced into thePacific IslandsandNew Zealand. They were also carried byAustronesian voyagersintoMadagascarand theComoros.
The center of origin of purple yam is inthe Philippines, but archaeological evidence suggests that it was exploited inIsland Southeast AsiaandNew Guineabefore 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 thePhilippinesandNew Guinea.
Based on archaeological evidence of early farming plots and plant remains in theKuk Swampsite, authors have suggested that it was first domesticated in the highlands of New Guinea from around 10,000BPand spread into Island Southeast Asia via theLapita cultureat around c. 4,000BP, along withD. nummulariaandD. bulbifera. In turn,D. esculentais 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.
However, much older remains identified as being probablyD. alatahave also been recovered from theNiah CavesofBorneo(Late Pleistocene, <40,000BP) and theIlle CaveofPalawan(c. 11,000BP), along with remains of the toxic ubi gadong (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. alatawere native to Island Southeast Asia. Furthermore, it opens the question on whetherD. alatais a true species or cultivated much older than believed.
Purple yam remains an important crop in Southeast Asia, particularly in thePhilippineswhere 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 easternPolynesiaandNew Zealand, however, has waned after the introduction of other crops, most notably thesweet potato.
Purple yams have edible tubers which have a mildly sweet, earthy and nutty taste, reminiscent ofsweet potatoesortaro. The violet cultivars, in particular, turn dishes distinctively vivid violet because of the high amount ofanthocyanins.Purple yams are also valued for thestarchthat can be processed from them.Purple yam is most common inPhilippine cuisine(where it is known asubeorubi). It is widely applied for many Philippine desserts, such asube cake,ube cheesecakeandube 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.Purple yam desserts have more recently entered theUnited Statesthrough Philippine cuisine, under the Filipino name "ube". It is particularly popular due to the striking violet-purple color it gives to desserts.
Purple yam is commonly confused with purple/violet varieties ofsweet potatoesbecause 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.
Although available as adietary supplementand used infolk medicine, there is noclinical evidencethatD. alatahas any therapeutic properties.Use ofD. alatasupplements may haveadverse effectsin people takingestrogens,anticoagulantdrugs or during pregnancy and breast-feeding.Some people may haveallergic reactionsto use ofD. alatasupplements.
D. alatahas relatively high levels ofoxalates(486–781 mg/100 g dry matter),which are associated withantinutritional effectsandkidney stoneformation.
The color of purple varieties is due to variousanthocyaninpigments.The pigments are water-soluble, and have been proposed as possiblefood coloringagents.D. alatais sometimes grown in gardens for its ornamental value.
Dioscorea alatais native to the Philippines, as well as surrounding areas (Taiwanand theRyukyu IslandsofJapan).  It has escaped from its native growth area and into the wild in many other places, becomingnaturalizedin parts of southern and east-centralChina,AfricaandMadagascar, theWestern Hemisphere, and various islands in theIndianandPacificoceans.It persists in the wild in Haiti, as well as theUnited States, inLouisiana,Georgia,Alabama,Puerto Rico, theU.S. Virgin Islands, and inFloridawhere it is considered aninvasive species.