View source for Yam (vegetable)

{{Short description|Edible starchy tuber}}
{{About|the large tuberous starchy root eaten as a staple food|the North American yam|Sweet potato|the New Zealand yam|Oxalis tuberosa{{!}}''Oxalis tuberosa''|elephant foot yam|Amorphophallus paeoniifolius{{!}}''Amorphophallus paeoniifolius''}}
{{Use dmy dates|date=April 2025}}
[[File:Yams species called Parkistan. The size is for eating but smaller sizes can be cultivated.jpg|thumb|Unknown yam variety, most likely of the ''alata'' species.]]
[[File:YamsatBrixtonMarket.jpg|thumb|White yams at a retail market in [[Brixton]], England, 2004]]

'''Yam''' is the common name for some plant species in the genus ''[[Dioscorea]]'' (family [[Dioscoreaceae]]) that form edible [[tuber]]s (some other species in the genus being toxic).

Yams are [[perennial]] [[herbaceous]] [[vine]]s native to Africa, Asia, and the Americas and cultivated for the consumption of their [[starch]]y tubers in many [[temperate climate|temperate]] and [[tropics|tropical]] regions. The tubers themselves, also called "yams", come in a variety of forms owing to numerous [[cultivar]]s and related species.
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== Description ==
[[File:കാച്ചിൽ-കിഴങ്ങ്.JPG|thumb|A yam]]

A [[Monocotyledon|monocot]] related to lilies and grasses, yams are vigorous [[herbaceous]],  [[perennial plant|perennial]]ly growing [[vine]]s from a [[tuber]].<ref name="cabi">{{cite web |date=2016 |title=''Dioscorea alata'' (white yam) |url=https://www.cabi.org/isc/datasheet/19293 |access-date=5 December 2017 |publisher=[[Centre for Agriculture and Bioscience International]] }}</ref> Some 870 species of yams are known,<ref name="cabi" /> a few of which are widely grown for their edible tuber but others of which are toxic (such as ''[[Dioscorea communis|D. communis]]'').

Yam plants can grow up to {{convert|15|m|ft|-1|abbr=off}} in length and {{convert|7|to|15|cm|in|frac=2|abbr=off}} high.<ref name="cabi" /> The tuber may grow into the soil up to {{convert|1.5|m|ft|abbr=on|frac=2}} deep.<ref name="cabi" /> The plant disperses by [[seed]].<ref name="cabi" />

The edible tuber has a rough skin that is difficult to peel but readily softened by cooking. The skins vary in color from dark brown to light pink. The majority, or meat, of the vegetable is composed of a much softer substance ranging in color from white or yellow to purple or pink in mature yams.

== Etymology ==
The name "yam" appears to derive from Portuguese ''inhame'' or [[Canarian Spanish]] ''ñame'', which derived from [[Fula language|Fula]], one of the [[West African languages]] during trade.<ref name="oed">{{cite dictionary |title=Yam |url=https://www.etymonline.com/word/yam |dictionary=[[Online Etymology Dictionary]] |publisher=[[Douglas Harper]] |date=2017 |access-date=5 December 2017 }}</ref> However, in Portuguese, this name commonly refers to the [[taro]] plant (''Colocasia esculenta'') from the genus ''[[Colocasia]]'', as opposed to ''Dioscorea''.<ref>{{cite web |title=Inhame dos Açores |url=https://tradicional.dgadr.gov.pt/pt/cat/outros-produtos-vegetais/771-inhame-dos-acores |publisher=[[Produtos Tradicionais Portugueses]] |date=2020 |access-date=13 August 2020 }}</ref><ref>{{cite web |title=Sabores dos Açores: Inhame |url=https://www.clubevinhosportugueses.pt/turismo/sabores-dos-acores-inhame/ |publisher=[[Clube Vinhos Portugueses]] |date=2020 |access-date=13 August 2020 }}</ref>

The main derivations borrow from verbs meaning "to eat".<ref name="oed" /> True yams have various [[common names]] across multiple world regions.<ref name="cabi" />

In some places, other (unrelated) root vegetables are sometimes referred to as "yams", including:<ref name="cabi" />
* In the United States, [[sweet potatoes]] (''[[Ipomoea]] batatas''), especially those with orange flesh, are often referred to as "yams"<ref>{{cite web |url=https://www.loc.gov/rr/scitech/mysteries/sweetpotato.html |website=LOC.gov |title=What is the difference between sweet potatoes and yams?}}</ref><ref>{{cite web |url=http://www.ers.usda.gov/publications/agoutlook/Nov2002/ao296e.pdf |title=Economic Research Service |access-date=26 November 2009 |archive-date=15 March 2015 |archive-url=https://web.archive.org/web/20150315002720/http://www.ers.usda.gov/publications/agoutlook/Nov2002/ao296e.pdf |url-status=dead }}</ref>
* In Australia, the tubers of the ''[[Microseris walteri]]'', or yam daisy, were a staple food of [[Aboriginal Australians]] in some regions.<ref>{{Cite book|title=Dark Emu, Black Seeds: Agriculture or Accident?|last=Pascoe|first=Bruce|publisher=[[Magabala Books]]|date=2014|isbn=978-1-922142-43-6|pages=22–24}}</ref> 
* In New Zealand, oca (''[[Oxalis tuberosa]]'') is typically referred to as "yam".<ref>[http://www.garden-nz.co.nz/grow-your-own/grow-your-own/yams-grow-your-own.html ''"...but in New Zealand we call them yams."'']{{Dead link|date=March 2025 |bot=InternetArchiveBot |fix-attempted=yes }}, garden-nz.co.nz</ref><ref name="jsfa">{{cite journal |journal=[[Journal of the Science of Food and Agriculture]]|author1=Albihn, P.B.E. |author2=Savage, G.P. |date=18 June 2001 |title=The effect of cooking on the location and concentration of oxalate in three cultivars of New Zealand-grown oca (''Oxalis tuberosa'' Mol) |volume=81 |pages=1027–1033 |doi= 10.1002/jsfa.890 |issue=10 |bibcode=2001JSFA...81.1027A }}</ref>
* In [[Malaysia]] and [[Singapore]], [[taro]] (''Colocasia esculenta'') is referred to as "yam".<ref>{{cite web |url=http://thestar.com.my/english/story.asp?file=/2010/7/16/lifefocus/6651716&sec=lifefocus |title=I yam not taro |first=Lim Chin|last=Lam |website=[[The Star (Malaysia)|The Star]]}}</ref>
* In Africa, South and Southeast Asia as well as the tropical Pacific islands ''[[Amorphophallus paeoniifolius]]'' is grown and known as "elephant foot yam".<ref>{{cite journal |last1=Santosa |first1=Edi |last2=Lian |first2=Chun Lan |last3=Sugiyama |first3=Nobuo |last4=Misra |first4=Raj Shekhar |last5=Boonkorkaew |first5=Patchareeya |last6=Thanomchit |first6=Kanokwan |last7=Chiang |first7=Tzen-Yuh |title=Population structure of elephant foot yams (''Amorphophallus paeoniifolius'' (Dennst.) Nicolson) in Asia |journal=[[PLOS ONE]] |date=28 June 2017 |volume=12 |issue=6 |page=e0180000 |doi=10.1371/journal.pone.0180000 |pmid=28658282 |pmc=5489206 |bibcode=2017PLoSO..1280000S |display-authors=1 |doi-access=free }}</ref>

==Distribution and habitat==
Yams are native to Africa, Asia, and the Americas.<ref name="cabi" /> Three species were independently domesticated on those continents: ''[[Dioscorea rotundata|D. rotundata]]'' (Africa), ''[[Dioscorea alata|D.&nbsp;alata]]'' (Asia), and ''[[Dioscorea trifida|D.&nbsp;trifida]]'' (South America).<ref>{{cite journal |last1=Nora Scarcelli |display-authors=etal |date=1 May 2019 |title=Yam genomics supports West Africa as a major cradle of crop domestication |journal=[[Science Advances]] |volume=5 |issue=5 |pages=eaaw1947 |bibcode=2019SciA....5.1947S |doi=10.1126/sciadv.aaw1947 |pmc=6527260 |pmid=31114806 |doi-access=free }}</ref>

==Ecology==
Some yams are [[invasive plant]]s, often considered a [[noxious weed]] outside cultivated areas.<ref name="cabi" />

==Cultivation==
[[File:Kaachil cut.jpg|thumb|Freshly harvested purple yam (''[[Dioscorea alata|D.&nbsp;alata]]'') sliced for cross-section]]

Yams are cultivated for the consumption of their [[starch]]y tubers in many [[temperate climate|temperate]] and [[tropics|tropical]] regions, especially in West Africa, South America and the [[Caribbean]], Asia, and [[Oceania]].<ref name="cabi" /> About 95% of yam crops are grown in Africa.<ref>{{cite web |date=2011 |title=Everyday Mysteries: Yam |url=https://www.loc.gov/rr/scitech/mysteries/sweetpotato.html |publisher=Library of Congress, United States of America}}</ref>

A yam crop begins when whole seed tubers or tuber portions are planted into mounds or ridges, at the beginning of the rainy season. The crop yield depends on how and where the sets are planted, sizes of mounds, interplant spacing, provision of stakes for the resultant plants, yam species, and tuber sizes desired at harvest. Small-scale farmers in West and Central Africa often [[wikt:intercrop|intercrop]] yams with cereals and vegetables. The seed yams are perishable and bulky to transport. Farmers who do not buy new seed yams usually set aside up to 30% of their harvest for planting the next year. Yam crops face pressure from a range of insect pests and fungal and viral diseases, as well as [[nematode|nematodes]]. Their growth and dormant phases correspond respectively to the wet season and the dry season. For maximum yield, the yams require a humid tropical environment, with an annual rainfall over {{Convert|1500|mm|in|0}} distributed uniformly throughout the growing season. White, yellow, and water yams typically produce a single large tuber per year, generally weighing {{convert|5|to|10|kg|lb|0|abbr=off}}.<ref name="stofao1" />

Yams suffer from relatively few pests and diseases.<ref name="Solomon" /> There is an {{Visible anchor|Anthracnose|text=[[anthracnose]]}} caused by ''[[Colletotrichum gloeosporioides]]'' which is widely distributed around the world's growing regions.<ref name="Solomon" /> Winch ''et al.'', 1984 finds ''C.&nbsp;gloeosporioides'' afflicts a large number of ''Dioscorea'' spp.<ref name="Solomon">
{{Cite journal
 |last1=Winch |first1=J. E.
 |last2=Newhook |first2=F. J.
 |last3=Jackson |first3=G. V. H.
 |last4=Cole |first4=J. S.
 |date=1984
 |title=Studies of Colletotrichum gloeosporioides disease on yam, Dioscorea alata, in Solomon Islands
 |journal=[[Plant Pathology (journal)|Plant Pathology]]
 |volume=33 |issue=4 |pages=467–477
 |doi=10.1111/j.1365-3059.1984.tb02870.x
|bibcode=1984PPath..33..467W
 }}
As cited in {{cite book
 |last1=O'Hair |first1=Stephen K.
 |date=1990
 |chapter=Tropical Root and Tuber Crops
 |editor-last=Janick |editor-first=Jules
 |title=Horticultural Reviews
 |volume=12
 |pages=181–182
 |publisher=[[Timber Press]]
 |doi=10.1002/9781118060858.ch3
 |isbn=9781118060858
}}
</ref>

Despite the high labor requirements and production costs, consumer demand for yam is high in certain subregions of Africa,<ref name=cabi/> making yam cultivation quite profitable to certain farmers.<ref>{{Cite web |title=PubMed Central (PMC) |url=https://pmc.ncbi.nlm.nih.gov/ |access-date=2025-06-07 |website=PubMed Central (PMC) |language=en}}</ref>

=== Major cultivated species ===
Many cultivated species of ''Dioscorea'' yams are found throughout the humid tropics.<ref name=cabi/> The most economically important are discussed below.<ref name=stofao1>{{cite web|title=Storage and Processing of Roots and Tubers in the Tropics|publisher=United Nations [[Food and Agriculture Organization]]|author=Calverly|date=1998|url=http://www.fao.org/docrep/X5415E/x5415e00.htm}}</ref>

Non-''[[Dioscorea]]'' tubers that were historically important in Africa include ''[[Plectranthus rotundifolius]]'' (the Hausa potato) and ''[[Plectranthus esculentus|P. esculentus]]'' (the Livingstone potato); these two tuber crops have now been largely displaced by the introduction of [[cassava]].<ref name="AfricanPast">{{Cite book|title=Archaeology, language, and the African past|last=Blench|first=Roger|publisher=[[Altamira Press]]|date=2006|isbn=9780759104655}}</ref>

==== ''D. rotundata'' and ''D. cayennensis'' ====
''[[Dioscorea rotundata|D. rotundata]]'', the white yam, and ''[[Dioscorea cayenensis|D. cayenensis]]'', the yellow yam, are native to Africa. They are the most important cultivated yams. In the past, they were considered as two separate species, but most taxonomists now regard them as the same species. Over 200 varieties between them are cultivated.<ref>{{cite book
|title=Yams, Dioscorea spp.
|editor=Agnes Pothier (Ed.)
|chapter=Major Cultivated Species – D. rotundata and D. cayenensis
|publisher=Springer
|year=2010
|pages=Fig. 5.1–5.2
}}</ref>

White yam tuber is roughly cylindrical in shape, the skin is smooth and brown, and the flesh is usually white and firm. Yellow yam has yellow flesh, caused by the presence of carotenoids. It looks similar to the white yam in outer appearance; its tuber skin is usually a bit firmer and less extensively grooved. The yellow yam has a longer period of vegetation and a shorter dormancy than white yam.

The [[Kokoro (vegetable)|Kokoro]] variety is important in making dried yam chips.<ref>{{Cite journal |last1=Dumont |first1=R. |last2=Vernier |first2=P. |date=2000 |doi=10.5367/000000000101293149 |title=Domestication of yams (''Dioscorea cayenensis-rotundata'') within the Bariba ethnic group in Benin |journal=[[Outlook on Agriculture]]|volume=29 |issue=2 |page=137|bibcode=2000OutAg..29..137D |s2cid=154609802 }}</ref>

They are large plants; the vines can be as long as {{convert|10|to|12|m|ft|0|abbr=on}}. The tubers most often weigh about {{convert|2.5|to|5|kg|lb|0|abbr=on}} each, but can weigh as much as {{convert|25|kg|lb|0|abbr=on}}. After 7 to 12 months' growth, the tubers are harvested. In Africa, most are pounded into a paste to make the traditional dish of "pounded yam", known as [[Iyan]].<ref name="kay">{{cite book |author=Kay, D.E. |date=1987 |title=Root Crops |publisher=[[Tropical Development and Research Institute]]|location=[[London, UK]]}}</ref>

==== ''D. alata'' ====
[[File:Yam with numerous protruding fibers.jpg|thumb|Purple yam (''D. alata'')]]

''[[Dioscorea alata|D. alata]]'', called purple yam (not to be confused with the Okinawan purple "yam", which is a [[sweet potato]]), greater yam, winged yam, water yam, and (ambiguously) white yam,<ref name="Thompson">{{cite book |last1=Thompson |first1=Anthony Keith |title=Fruit and Vegetables: Harvesting, Handling and Storage |date=2014 |publisher=[[John Wiley & Sons]]|isbn=9781118654019}}</ref><ref name=cabi/> was first cultivated in Southeast Asia.<ref name=cabi/> Although not grown in the same quantities as the African yams, it has the largest distribution worldwide of any cultivated yam, being grown in Asia, the Pacific islands, Africa, and the West Indies.<ref name=cabi/> Even in Africa, the popularity of water yam is second only to white yam. The tuber shape is generally cylindrical, but can vary. Tuber flesh is white and watery in texture.

''D. alata'' and ''D. esculenta'' (lesser yam) were important staple crops to the seafaring [[Austronesian peoples|Austronesian]] cultures. They were carried along with the Austronesian migrations as [[canoe plants]], from [[Island Southeast Asia]] to as far as [[Madagascar]] and [[Polynesia]].<ref name="Crowther2016">{{cite journal |last1=Crowther |first1=Alison |last2=Lucas |first2=Leilani |last3=Helm |first3=Richard |last4=Horton |first4=Mark |last5=Shipton |first5=Ceri |last6=Wright |first6=Henry T. |last7=Walshaw |first7=Sarah |last8=Pawlowicz |first8=Matthew |last9=Radimilahy |first9=Chantal |last10=Douka |first10=Katerina |last11=Picornell-Gelabert |first11=Llorenç |last12=Fuller |first12=Dorian Q. |last13=Boivin |first13=Nicole L. |title=Ancient crops provide first archaeological signature of the westward Austronesian expansion |journal=[[Proceedings of the National Academy of Sciences]]|date=14 June 2016 |volume=113 |issue=24 |pages=6635–6640 |doi=10.1073/pnas.1522714113 |pmid=27247383 |pmc=4914162|bibcode=2016PNAS..113.6635C |doi-access=free }}</ref><ref name="Beaujard2011">{{cite journal |last1=Beaujard |first1=Philippe |title=The first migrants to Madagascar and their introduction of plants: linguistic and ethnological evidence |journal=[[Azania: Archaeological Research in Africa]] |date=August 2011 |volume=46 |issue=2 |pages=169–189 |doi=10.1080/0067270X.2011.580142 |s2cid=55763047 |url=https://halshs.archives-ouvertes.fr/halshs-00706173/file/Beaujard.azania2.pdf}}</ref><ref name="Bevacqua1994">{{cite journal |last1=Bevacqua |first1=Robert F. |title=Origin of Horticulture in Southeast Asia and the Dispersal of Domesticated Plants to the Pacific Islands by Polynesian Voyagers: The Hawaiian Islands Case Study |journal=[[HortScience]]|date=1994 |volume=29 |issue=11 |pages=1226–1229 |url=http://hortsci.ashspublications.org/content/29/11/1226.full.pdf |doi=10.21273/HORTSCI.29.11.1226 |doi-access=free}}</ref><ref>{{cite web |last=White |first=L.D. |date=2003 |url=http://www.canoeplants.com/uhi.html |series=Canoe Plants of Ancient Hawai'i |title=Uhi}}</ref>

==== ''D. polystachya'' ====
[[File:Dioscorea polystachya (batatas).jpg|thumb|[[Chinese yam]] (''D. polystachya'')|alt=Segment of a [[Chinese yam]] (''D. polystachya'')]]

''[[Dioscorea polystachya|D. polystachya]]'', Chinese yam, is native to [[China]]. The Chinese yam plant is somewhat smaller than the African, with the vines about {{convert|3|m|ft|0|abbr=on}} long. It is tolerant to frost and can be grown in much cooler conditions than other yams. It is also grown in [[Korea]] and [[Japan]].

It was introduced to [[Europe]] in the 19th century, when the [[potato]] crop there was falling victim to disease, and is still grown in France for the Asian food market.

The tubers are harvested after about 6 months of growth. Some are eaten right after harvesting and some are used as ingredients for other dishes, including noodles, and for traditional medicines.<ref name="kay" />

==== ''D. bulbifera'' ====
[[File:Starr 030807-0054 Dioscorea bulbifera.jpg|thumb|upright|Air potato (''D. bulbifera'')]]
[[File:MS 1960.JPG|thumb|right|Wild yam (''D.'' sp.)]]

''[[Dioscorea bulbifera|D. bulbifera]]'', the air potato, is found in both Africa and Asia, with slight differences between those found in each place. It is a large vine, {{convert|6|m|ft|0|abbr=on}} or more in length. It produces tubers, but the [[bulb]]ils which grow at the base of its leaves are the more important food product. They are about the size of potatoes (hence the name "air potato"), weighing from {{convert|0.5|to|2.0|kg|lboz|abbr=on}}.

Some varieties can be eaten raw, while some require soaking or boiling for detoxification before eating. It is not grown much commercially since the flavor of other yams is preferred by most people. However, it is popular in home vegetable gardens because it produces a crop after only four months of growth and continues producing for the life of the vine, as long as two years. Also, the bulbils are easy to harvest and cook.<ref name="kay" />

In 1905, the air potato was introduced to Florida and has since become an [[invasive species]] in much of the state. Its rapid growth crowds out native vegetation and it is very difficult to remove since it can grow back from the tubers, and new vines can grow from the bulbils even after being cut down or burned.<ref name="schultz">{{cite web |last=Schultz |first=G.E. |date=1993 |title=Element Stewardship Abstract for ''Dioscorea bulbifera'', Air potato |url=http://tncweeds.ucdavis.edu/esadocs/documnts/diosbul.html |publisher=Nature Conservancy |access-date=2 September 2006 |archive-date=18 September 2006 |archive-url=https://web.archive.org/web/20060918184430/http://tncweeds.ucdavis.edu/esadocs/documnts/diosbul.html |url-status=dead }}</ref>

==== ''D. esculenta'' ====
[[File:Dioscorea Bild1162.jpg|thumb|Wild bitter vines (''[[Dioscorea dumetorum|D. dumetorum]]'')|alt=Wild bitter yam vines (''D. dumetorum'')]]

''[[Dioscorea esculenta|D. esculenta]]'', the lesser yam, was one of the first yam species cultivated. It is native to Southeast Asia and is the third-most commonly cultivated species there, although it is cultivated very little in other parts of the world. Its vines seldom reach more than {{convert|3|m|ft|0|abbr=on}} in length and the tubers are fairly small in most varieties.

The tubers are eaten baked, boiled, or fried much like potatoes. Because of the small size of the tubers, mechanical cultivation is possible, which along with its easy preparation and good flavor, could help the lesser yam to become more popular in the future.<ref name="kay" />

==== ''D. dumetorum'' ====
''[[Dioscorea dumetorum|D. dumetorum]]'', the bitter yam, is popular as a vegetable in parts of West Africa, in part because their cultivation requires less labor than other yams. The wild forms are very toxic and are sometimes used to poison animals when mixed with bait. It is said{{according to whom|date=December 2019}} that they have also been used for criminal purposes.<ref name="kay" />

==== ''D. trifida'' ====
''[[Dioscorea trifida|D. trifida]]'', the cush-cush yam, is native to the [[Guyana]] region of South America and is the most important cultivated New World yam. Since they originated in tropical [[rainforest]] conditions, their growth cycle is less related to seasonal changes than other yams. Because of their relative ease of cultivation and their good flavor, they are considered to have a great potential for increased production.<ref name="kay" />

===Wild taxa===

====''D. hirtiflora'' subsp. ''pedicellata''==== 
''[[Dioscorea hirtiflora|D. hirtiflora]]'' subsp. ''pedicellata'', lusala, busala or lwidi, is native to [[Tropical Africa]]. It is widely harvested and eaten in Southern Zambia where it grows in open forest areas. In Southern Zambia, it is an important addition to the March–September diets of almost all, and income of over half of rural households.<ref name="Zulu">{{cite journal | last1=Zulu | first1=Donald | last2=Ellis | first2=Richard H. | last3=Culham | first3=Alastair | title=Collection, Consumption, and Sale of Lusala (''Dioscorea hirtiflora'') — a Wild Yam — by Rural Households in Southern Province, Zambia | journal=[[Economic Botany]]| volume=73 | issue=1 | date=25 January 2019 | issn=0013-0001 | doi=10.1007/s12231-018-9433-3 | pages=47–63| doi-access=free | bibcode=2019EcBot..73...47Z }}</ref> Research on propagation of this subspecies to alleviate the threat from wild harvest has been successful.<ref>{{cite journal |doi=10.1017/S0014479720000083|title=Propagation of lusala (''Dioscorea hirtiflora''), a wild yam, for ''in situ'' and ''ex situ'' conservation and potential domestication |date=2020 |last1=Zulu |first1=D. |last2=Ellis |first2=R. H. |last3=Culham |first3=A. |journal=[[Experimental Agriculture]] |volume=56 |issue=3 |pages=453–468 |s2cid=216212360 |doi-access=free }}</ref>

====''D. japonica''==== 
''[[Dioscorea japonica|D. japonica]]'' {{endash}} known as East Asian mountain yam, yamaimo, or Japanese mountain yam {{endash}} is a type of yam (Dioscorea) native to Japan. Its other common names include cham ma, Chinese yam, dang ma, glutinous yam, jinenjo, pinyin, rìběn- shǔyù, shan yao, Taiwanese yam, and wild yam. Varieties include ''D. japonica'' Thunb var. ''pseudojaponica'' Yamamoto, ''D. japonica'' Thunb. var. ''pseudojaponica'' (Hayata) Yamam, ''D. japonica'' var. ''japonica'', ''D. japonica'' var. ''oldhamii'' and ''D. japonica'' var. ''pilifera''. It is widely cultivated Japan, Korea, China, and neighbouring islands.<ref name=":0">{{Cite book |last1=Thompson |first1=Anthony Keith |title=Yams: Botany, Production and Uses |last2=Oduro |first2=Ibok |publisher=[[Centre for Agriculture and Bioscience International|CABI]] |date=2021 |isbn=9781789249279 |location=Oxford |pages=172}}</ref> 

It is widely cultivated as a food crop in Japan, Korea, China and neighbouring islands.<ref name=":0" /> Jinenjo is a related variety of Japanese yam that is used as an ingredient in soba noodles.

=== Harvesting ===
[[File:Tile on street depicting Aboriginal women gathering yams. Cooktown, Australia. 2005.jpg|thumb|Tile on street depicting Aboriginal women gathering yams. [[Cooktown, Australia]]. 2005]]

Yams in [[West Africa]] are typically harvested by hand, using sticks, spades, or diggers.<ref name=opara /> Wood-based tools are preferred to metallic tools as they are less likely to damage the fragile tubers; however, wood tools need frequent replacement. Yam harvesting is labor-intensive and physically demanding. Tuber harvesting involves standing, bending, [[Squatting position|squatting]], and sometimes sitting on the ground depending on the size of mound, size of tuber, or depth of tuber penetration. Care must be taken to avoid damage to the tuber, because damaged tubers do not store well and spoil rapidly. Some farmers use staking and mixed cropping, a practice that complicates harvesting in some cases.

In forested areas, tubers grow in areas where other tree roots are present. Harvesting the tuber then involves the additional step of freeing them from other roots. This often causes tuber damage.

Aerial tubers or bulbils are harvested by manual plucking from the vine.

Yields may improve and cost of yam production be lower if mechanization were to be developed and adopted. However, current crop production practices and species used pose considerable hurdles to successful mechanization of yam production, particularly for small-scale rural farmers. Extensive changes in traditional cultivation practices, such as mixed cropping, may be required. Modification of current tuber harvesting equipment is necessary given yam tuber architecture and its different physical properties.<ref name=opara>{{cite web |title=YAMS: Post-Harvest Operation |author=Linus Opara |date=2003 |url=http://www.fao.org/fileadmin/user_upload/inpho/docs/Post_Harvest_Compendium_-_Yams.pdf}}</ref>

=== Production ===
{{Further|Yam production in Nigeria}}

In 2020, world production of yams was {{Convert|75|e6MT|abbr=off}}, led by [[Nigeria]] with 67% of the total (table).

{| class="wikitable floatright"
|+ Yam production in 2020
|-
! Country
! abbr="Production" | Production<br /><small>(millions of [[tonne]]s)</small>
|-
| {{NGA}} ||{{right|50.1}}
|-
| {{GHA}} ||{{right|8.5}}
|-
| {{CIV}} ||{{right|7.7}}
|-
| {{BEN}} ||{{right|3.2}}
|-
| {{TOG}} ||{{right|0.9}}
|-
| {{CMR}} ||{{right|0.7}}
|-
| '''World'''||{{right|'''74.8'''}}
|-
|colspan="2" style="font-size:90%;"|Source:UN Food and Agriculture Organization<ref name="faostat">{{cite web |url=http://www.fao.org/faostat/en/#data/QC |title=Yam production in 2019 |series=Crops/Regions/World/Production Quantity |publisher=[[FAOSTAT]], Statistics Division of the UN Food and Agriculture Organization |date=2021 |access-date=12 October 2021 }}</ref>
|}
[[File:Yamoutput.png|thumb|center|Map of worldwide yam production showing limited production range (Caribbean, West Africa, and Polynesia)]]
{{clear}}

== Toxicity ==
{{More citations needed|section|date=December 2017}}

Unlike [[cassava]], most varieties of edible, mature, cultivated yam do not contain toxic compounds. However, there are exceptions. Bitter compounds tend to accumulate in immature tuber tissues of white and yellow yams.{{citation needed|date=April 2025}}

Wild forms of bitter yams (''[[Dioscorea dumetorum|D. dumetorum]]'') do contain some toxins, such as [[dihydrodioscorine]], that taste bitter, hence are referred to as bitter yam.<ref>[http://tropical.theferns.info/viewtropical.php?id=Dioscorea+dumetorum ''Dioscorea dumetorum'': Useful Tropical Plants]</ref> Bitter yams are not normally eaten except at times of desperation in poor countries and in times of local food scarcity. They are usually detoxified by soaking in a vessel of salt water, in cold or hot fresh water or in a stream. The bitter compounds in these yams are water-soluble alkaloids which, on ingestion, produce severe and distressing symptoms. Severe cases of alkaloid intoxication may prove fatal.{{Citation needed|date=November 2021}}

Aerial or potato yams (''D. bulbifera'') have antinutritional factors. In Asia, detoxification methods, involving water extraction, fermentation, and roasting of the grated tuber, are used for bitter cultivars of this yam. The bitter compounds in yams also known locally as air potato include diosbulbin and possibly [[saponin]]s, such as [[diosgenin]].<ref name="jesus">{{cite journal |last1=Jesus |first1=M. |last2=Martins |first2=A. P |last3=Gallardo |first3=E. |last4=Silvestre |first4=S. |date=2016 |title=Diosgenin: Recent Highlights on Pharmacology and Analytical Methodology |journal=[[Journal of Analytical Methods in Chemistry]] |volume=2016 |pages=1–16 |doi=10.1155/2016/4156293 |pmc=5225340 |pmid=28116217 |doi-access=free }}</ref> In Indonesia, an extract of air potato is used in the preparation of arrow poison.<ref name="fao1990a">{{cite book |last=Oke |first=O.L. |url=https://archive.org/details/rootstubersplant0000unse |title=Roots, tubers, plantains and bananas in human nutrition |publisher=United Nations [[Food and Agriculture Organization]] |date=1990 |isbn=978-92-5-102862-9 |editor1=Redhead, J. |editor2=Hussain, M.A. |url-access=registration }}</ref>

== Uses ==

=== Nutrition ===
{{Nutritionalvalue
| name = Yam, raw
| kJ = 494
| protein = 1.5 g
| fat = 0.17 g
| carbs = 27.9 g
| fiber = 4.1 g
| sugars = 0.5 g
| calcium_mg = 17
| iron_mg = 0.54
| magnesium_mg = 21
| phosphorus_mg = 55
| potassium_mg = 816
| zinc_mg = 0.24
| manganese_mg = 0.397
| vitC_mg = 17.1
| thiamin_mg = 0.112
| riboflavin_mg = 0.032
| niacin_mg = 0.552
| pantothenic_mg = 0.314
| vitB6_mg = 0.293
| folate_ug = 23
| vitA_ug = 7
| vitE_mg = 0.35
| vitK_ug = 2.3
| source_usda = 1
| note = {{cite web |url=https://fdc.nal.usda.gov/food-details/170071/nutrients |title=Link to USDA Database entry |access-date=19 October 2022 |archive-date=3 April 2019 |archive-url=https://web.archive.org/web/20190403171801/https://fdc.nal.usda.gov/fdc-app.html#/food-details/170071/nutrients |url-status=live }}
}}

Raw yam has only moderate [[nutrient density]], with ''appreciable content'' (10% or more of the [[Daily Value]], DV) limited to [[potassium]], [[vitamin B6]], [[manganese]], [[thiamin]], [[dietary fiber]], and [[vitamin C]] (table).<ref>{{cite book|title=Postharvest technology and commodity marketing: Proceedings of a postharvest conference |date=1998 |isbn=978-978-131-111-6 |page=172 |author=Uwaegbute, Osho and Obatolu|publisher=International Institute of Tropical Agriculture}}</ref> But raw yam has the highest potassium levels amongst the 10 major staple foods of the world ([[Yam (vegetable)#Comparison to other staple foods|see nutritional chart]]). Yam supplies {{convert|494|kJ|kcal|abbr=off}} of [[food energy]] per 100 grams. Yam generally has a lower [[glycemic index]], about 54% of [[glucose]] per 150-gram serving, compared to potato products.<ref>{{cite web |url=http://www.health.harvard.edu/newsweek/Glycemic_index_and_glycemic_load_for_100_foods.htm |title=Glycemic index and glycemic load for 100+ foods |series=[[Harvard Health Publications]]|publisher=[[Harvard Medical School]]|date=2008}}</ref>

The protein content and quality of roots and tubers is lower than other food staples, with the content of yam and potato  being around 2% on a fresh-weight basis. Yams, with [[cassava]], provide a much greater proportion of the protein intake in Africa, ranging from 5.9% in East and South Africa to about 15.9% in humid West Africa.<ref>{{Cite web|title=Roots, tubers, plantains and bananas in human nutrition - Nutritive value|url=http://www.fao.org/3/t0207e/T0207E05.htm|website=United Nations [[Food and Agriculture Organization]] |access-date=25 May 2020}}</ref>

As a relatively low-protein food, yam is not a good source of [[essential amino acid]]s. Experts emphasize the need to supplement a yam-dominant diet with more protein-rich foods to support healthy growth in children.<ref>{{cite web |title=Kwashiorkor (Protein-Calorie Malnutrition) |publisher=[[Tropical Medicine Central Resource]] |date=2006 |url=http://tmcr.usuhs.mil/tmcr/chapter16/Kwashiorkor.htm |access-date=21 January 2012 |archive-date=16 December 2011 |archive-url=https://web.archive.org/web/20111216232523/http://tmcr.usuhs.mil/tmcr/chapter16/Kwashiorkor.htm |url-status=dead }}</ref><ref>{{cite web |title=Undernutrition |publisher=The [[Merck Manual]]: The Home Health Handbook |date=2010 |url=http://www.merckmanuals.com/home/disorders_of_nutrition/undernutrition/undernutrition.html}}</ref>

Yam is an important dietary element for Nigerian and West African people. It contributes more than 200 calories per person per day for more than 150 million people in West Africa, and is an important source of income. Yam is an attractive crop in poor farms with limited resources. It is rich in starch, and can be prepared in many ways. It is available all year round, unlike other, unreliable, seasonal crops. These characteristics make yam a preferred food and a culturally important food security crop in some sub-Saharan African countries.<ref>{{cite journal |title=Determinants of yam production and profitability in Edo State, Nigeria |author=OB Izekor |author2=MI Olumese |journal=[[African Journal of General Agriculture]]|volume=6 |number=4 |date=December 2010 |url=http://www.asopah.org/journals/ajga/ajga6/ajga640310091.pdf |archive-url=https://web.archive.org/web/20170517063405/http://www.asopah.org/journals/ajga/ajga6/ajga640310091.pdf|archive-date=17 May 2017}}</ref>

==== Comparison to other staple foods ====
The following table shows the nutrient content of yam and major staple foods in a raw harvested form on a [[Dry matter#Dry matter basis|dry weight basis]] to account for their different water contents. Raw forms, however, are not edible and cannot be digested. These must be sprouted, or prepared and cooked for human consumption. In sprouted or cooked form, the relative nutritional and antinutritional contents of each of these staples is remarkably different from that of raw form of these staples.<ref>{{Cite web |title=Yam, raw nutrition facts and analysis. |url=https://www.nutritionvalue.org/Yam%2C_raw_nutritional_value.html |access-date=2025-06-30 |website=www.nutritionvalue.org}}</ref>
{{Comparison of major staple foods}}

=== Storage ===
Roots and tubers such as yam are living organisms. When stored, they continue to respire, which results in the oxidation of the [[starch]] (a polymer of glucose) contained in the cells of the tuber, which converts it into water, [[carbon dioxide]], and heat energy. During this transformation of the starch, the dry matter of the tuber is reduced.

Amongst the major roots and tubers, properly stored yam is considered to be the least perishable. Successful storage of yams requires:<ref name="fao1990a" /><ref>{{Cite book |title=Roots, Tubers, and Plantains in Food Security: In Sub-Saharan Africa, in Latin America and the Caribbean, in the Pacific |publisher=United Nations [[Food and Agriculture Organization]] |year=1989 |isbn=978-92-5-102782-0}}</ref>
* initial selection of sound and healthy yams
* proper curing, if possible combined with fungicide treatment
* adequate ventilation to remove the heat generated by respiration of the tubers
* regular inspection during storage and removal of rotting tubers and any sprouts that develop
* protection from direct sunlight and rain

Storing yam at low temperature reduces the respiration rates. However, temperatures below {{convert|12|C}} cause damage through chilling, causing a breakdown of internal tissues, increasing water loss and yam's susceptibility to decay. The symptoms of chilling injury are not always obvious when the tubers are still in cold storage. The injury becomes noticeable as soon as the tubers are restored to ambient temperatures.

The best temperature to store yams is between {{convert|14|and|16|C}}, with high-technology-controlled humidity and climatic conditions, after a process of curing. Most countries that grow yams as a staple food are too poor to afford high-technology storage systems.

Sprouting rapidly increases a tuber's respiration rates, and accelerates the rate at which its food value decreases.<ref name="fao1990a" />

Certain cultivars of yams store better than others. The easier to store yams are those adapted to arid climate, where they tend to stay in a dormant low-respiration stage much longer than yam breeds adapted to humid tropical lands, where they do not need dormancy. Yellow yam and cush-cush yam, by nature, have much shorter dormancy periods than water yam, white yam, or lesser yam.

[[Storage loss]]es for yams are very high in Africa, with bacteria, insects, nematodes, and mammals being the most common [[storage pest]]s.<ref>
{{Cite book |last1=Robertson |first1=Gordon |last2=Lupien |first2=John |date=2008 |title=Using food science and technology to improve nutrition and promote national development: Selected case studies |publisher=[[International Union of Food Science & Technology]] |chapter=Minimizing Postharvest Losses in Yam (Dioscorea spp.): Treatments and Techniques |chapter-url=https://www.researchgate.net/publication/259999490 |s2cid=107695924 }}</ref>{{RP|1,7}}

=== Consumption ===
{{More citations needed|section|date=June 2017}}
[[File:Igname frite2.jpg|thumb|Yams being fried in [[Ivory Coast]]]]

Yams are consumed in a variety of preparations, such as flour or whole vegetable pieces across their range of distribution in Asia, Africa, North America, [[Central America]], the [[Caribbean]], South America, and [[Oceania]].<ref name="cabi" />

==== Africa ====
{{Multiple image
| direction         = horizontal
| total_width       = 330
| image1            = Kiekie yams.jpg
| caption1          = [[Tonga]]
| alt1              = [[Tonga]]n farmer showing off his prize yams
| image2            = Fufuprep.jpg
| caption2          = [[Pounded yam|Pounding yam]], [[Democratic Republic of Congo|DR Congo]]
| alt2              = Young women preparing [[pounded yam]] (which includes mashed and pounded yam flour) in the [[Democratic Republic of Congo]].
}}

Yams of African species must be cooked to be safely eaten, because various natural substances in yams can cause illness if consumed raw. The most common cooking methods in [[West Africa|Western]] and [[Central Africa]] are by boiling, frying or roasting.<ref name="bmgf">{{cite web |author1=Nweke, Felix |author2=Aidoo, Robert |author3=Okoye, Benjamin |title=Yam Consumption Patterns in West Africa |url=https://agriknowledge.org/downloads/6969z081q |archive-url=https://web.archive.org/web/20181122052052/https://agriknowledge.org/downloads/6969z081q |url-status=usurped |archive-date=22 November 2018 |publisher=Bill and Melinda Gates Foundation |access-date=5 December 2017 |date=July 2013}}</ref>

Among the Akan of Ghana, boiled yam can be mashed with palm oil into ''eto'' in a similar manner to the plantain dish ''[[matoke]]'', and is served with eggs. The boiled yam can also be pounded with a traditional mortar and pestle to create a thick, starchy paste known as ''[[iyan]]'' (pounded yam) which is eaten with traditional sauces such as ''[[egusi]]'' and [[Oil palm|palm nut]] soup.<ref>{{Cite web |last=Sam |first=Christopher |date=2021-05-01 |title=Food and culture: A case study of Ghana's Etor/Otor (Recipe Included) |url=https://www.theafricandream.net/food-and-culture-a-case-study-of-ghanas-etor-otor-recipe-included/ |access-date=2025-06-30 |website=TheAfricanDream |language=en-US}}</ref><ref>{{Cite web |last=Mavis |first=Meals by |date=2022-01-01 |title=Yam Eto (Ghanaian Mashed Yams) |url=https://mealsbymavis.com/yam-eto-mashed-ghanaian-yams/ |access-date=2025-06-30 |website=Meals by Mavis |language=en-US}}</ref>

Another method of consumption is to leave the raw yam pieces to [[Drying (food)|dry in the sun]]. When dry, the pieces turn a dark brown color. These are then milled to create a brown powder known in Nigeria as ''elubo''. The powder can be mixed with boiling water to create a thick starchy paste, a kind of pudding known as [[amala (food)|''amala'']], which is then eaten with local soups and sauces.<ref>{{Cite web |last=Osinkolu |first=Lola |date=2021-08-27 |title=YAM {{!}} TRUE YAM {{!}} AFRICAN YAM |url=https://cheflolaskitchen.com/true-yam-african-yam/ |access-date=2025-06-30 |website=Chef Lola's Kitchen |language=en-US}}</ref>

Yams are a staple agricultural [[commodity]] in [[West Africa]] with cultural significance,<ref name="bmgf" /> where over 95% of the world's yam crop is harvested. Yams are still important for survival in these regions. Some varieties of these tubers can be stored up to six months without refrigeration, which makes them a valuable resource for the yearly period of food scarcity at the beginning of the [[rainy season|wet season]]. Yam cultivars are also cultivated in other humid tropical countries.<ref name="cabi" />

Yam is the main staple crop of the [[Igbo people|Igbos]] in south eastern Nigeria where for centuries it played a dominant role in both their agricultural and cultural life. It is celebrated with annual [[New Yam Festival of the Igbo|yam festivals]].<ref>{{Cite web |title=TRT Global - Nigeria: How New Yam Festival keeps Igbo's rooted traditions alive |url=https://trt.global/afrika-english/article/14554175 |access-date=2025-06-30 |website=trt.global |language=en-af}}</ref>

==== Brazil ====
Yams are particularly consumed in the coastal area of the [[Northeast Region, Brazil|Northeast region]], although they can be found in other parts of the country. In [[Pernambuco]] state, it is usually boiled and served cut in slices at breakfast, along with [[Requeijão|cheese spread]] or [[molasses]].{{Citation needed|date=November 2021}}

==== Colombia ====
In Colombia yam production has been specifically located in the [[Caribbean region of Colombia|Caribbean region]], where it has become a key product in the diet of the population of this area. In 2010, Colombia was among the 12 countries with the highest yam production worldwide, and ranked first in yield of tons per hectare planted. Although its main use is for food, several studies have shown its usefulness in the pharmaceutical industry and the manufacture of bioplastics. However, in Colombia, there is no evidence of the use of this product, other than food.<ref>{{Cite web|title=El cultivo de ñame en el Caribe colombiano|url=https://www.banrep.gov.co/es/node/26485|website=Banco de la República, Colombia|date=21 June 2012}}</ref>

==== Philippines ====
[[File:Vanuatu marché igname.JPG|thumb|Yams at [[Port-Vila]] market ([[Vanuatu]])]]
[[File:Ube Cake.jpg|thumb|A piece of cake made with ube (purple yam; [[Philippines]])]]

In the Philippines, the purple ''ube'' species of yam (''D.&nbsp;alata''), is eaten as a sweetened dessert called ''[[ube halaya]]'', and is also used as an ingredient in another Filipino dessert, ''[[halo-halo]]''. It is also used as a popular ingredient for ice cream.<ref>{{Cite web |title=More Than a Trend: The History of Ube and What It Means to the Filipino People |url=https://www.kapwagardens.com/blog/more-than-a-trend-the-history-of-ube |access-date=2025-06-30 |website=Kapwa Gardens |language=en-US}}</ref>

==== Vietnam ====
In Vietnam, yams are used to prepare dishes such as ''canh khoai mỡ'' or ''canh khoai từ''. This involves mashing the yam and cooking it until very well done. The yam root was traditionally used by peasants in Vietnam to dye cotton clothes throughout the Red River and Mekong delta regions as late as the mid-20th century, and is still used by others in the [[Sa Pa District|Sapa region]] of northern Vietnam.<ref>[https://kilomet109.com/our-ingredients-the-yam-root/ Yam Root Dye]</ref>

==== Indonesia ====
In Indonesia, the same purple yam is used for preparing desserts. This involves mashing the yam and mixing it with coconut milk and sugar. White- and off-white-fleshed yams are cut in cubes, cooked, lightly fermented, and eaten as afternoon snacks.{{Citation needed|date=November 2021}}

==== Japan ====
[[File:Yamakake.JPG|thumb|''[[Yamakake]]'', Japanese dish prepared from ''[[Tororo (food)|tororo]]'' (''[[Dioscorea polystachya|D.&nbsp;polystachya]]'') and ''[[maguro]]'' (tuna)]]

An exception to the cooking rule is the mountain yam (''[[Dioscorea polystachya]]''), known as ''nagaimo'' and can be further classified into ''ichōimo'' (lit. 'ginkgo-leaf yam'; kanji: 銀杏芋), or ''yamatoimo'' (lit. Yamato yam; kanji: [[wikt:大和芋|大和芋]]), depending on the root shape.{{Citation needed|date=November 2021}}

Mountain yam is eaten raw and grated, after only a relatively minimal preparation: the whole tubers are briefly soaked in a vinegar-water solution to neutralize irritant [[oxalate]] crystals found in their skin.{{Citation needed|date=April 2025}}

Another variety of yam, ''jinenjo'', is used in Japan as an ingredient in soba noodles. In Okinawa, purple yams (''[[Dioscorea alata]]'') are grown. This purple yam is popular as lightly deep-fried tempura, as well as being grilled or boiled. Additionally, the purple yam is a common ingredient of yam ice cream and cake with the signature purple color.{{Citation needed|date=April 2025}}

==== India ====
In central parts of India, the yam is prepared by being finely sliced, seasoned with spices, and deep fried. In Southern India, the vegetable is a popular accompaniment to rice dishes and curry. The purple yam, ''D. alata'', is also eaten in India, where it is also called the violet yam. Species may be called by the regional name "taradi", which can refer to ''[[Dioscorea belophylla|D. belophylla]]'',<ref>Singh, K.K. and Kaushal Kumar. [https://books.google.com/books?id=CGcMAQAAMAAJ&q=taradi+Dioscorea Ethnobotanical wisdom of Gaddi tribe in Western Himalaya]. 2000. p.18.</ref> ''[[Dioscorea deltoidea]]'',<ref>Rana, M., Kabra, A., Kabra, R., Rana, M. and Dhatwalia, V. 2015. [http://www.pharmatutorjournal.com/index.php/pt/article/view/272 Plant Species used by locals as Ethano - Medicine in Gohar Tehsil, Distt. Mandi Region of North Western Himalaya.] {{Webarchive|url=https://web.archive.org/web/20230907234858/http://www.pharmatutorjournal.com/index.php/pt/article/view/272|date=7 September 2023}} ''[[PharmaTutor]]''. 3, 4 (Apr. 2015), 47-52.</ref> and ''D. bulbifera''.<ref>{{cite journal |last1=Rajendra |first1=Gupta |title=Conservation and utilization of Indian Medicinal Plants|journal=[[Indian Journal of Plant Genetic Resources]]|date=1993 |volume=6 |issue=2 |url=https://www.indianjournals.com/ijor.aspx?target=ijor:ijpgr&volume=6&issue=2&article=005 |access-date=16 September 2021 |issn=0971-8184}}</ref> Digging and selling taradi is a major source of income in the region of [[Palampur]].<ref>{{cite magazine |first=Chiranjit |last=Parmar |title=Taradi |magazine=The Heirloom Gardener |date=2007 }}</ref>

==== Nepal ====
''Dioscorea'' root is traditionally eaten on ''Māgh Sankrānti'' (a midwinter festival) in Nepal.{{Citation needed|date=April 2025}}

==== Fiji Islands ====
Yam is, along with [[cassava]] and [[taro]], a staple food, and is consumed boiled, roasted in a [[Earth oven|lovo]], or steamed with fish or meat in [[curry]] sauce or [[coconut milk]] and served with rice. The cost of yam is higher due to the difficulty in farming and relatively low volume of production.<ref>{{cite web |author=Naleba, Mere |date=25 April 2015 |title=Million dollar aim |url=http://www.fijitimes.com/story.aspx?id=303378 |access-date=1 June 2017 |publisher=The [[Fiji Times]] Online }}</ref>

==== Jamaica ====
Because of their abundance and importance to survival, yams were highly regarded in [[Jamaica]]n ceremonies and constitute part of many traditional [[West Africa]]n ceremonies.<ref>{{cite book |title=Cooking, cuisine and class: A study in comparative sociology |last=Goody|first=Jack|date=1996 |isbn=978-0-521-28696-1|pages=78–81|publisher=Cambridge University Press }}</ref>

==== The West ====
Yam powder is available in [[Western world|the West]] from grocers specializing in African products, and may be used in a similar manner to [[Instant mashed potatoes|instant mashed potato]] powder, although preparation is a little more difficult because of the tendency of the yam powder to form lumps. The powder is sprinkled onto a pan containing a small amount of boiling water and stirred vigorously. The resulting mixture is served with a heated sauce, such as [[Tomato sauce|tomato]] and [[Chili sauce|chili]], poured onto it.

Skinned and cut frozen yams may also be available from specialty grocers.

=== Phytochemicals and use in medicine ===
The tubers of certain wild yams, including a variant of '[[Kokoro (vegetable)|Kokoro]]' yam and other species of ''Dioscorea'', such as ''[[Dioscorea nipponica]]'', are a source for the extraction of [[diosgenin]], a sapogenin steroid.<ref name="jesus" /> The extracted diosgenin is used for the commercial synthesis of [[cortisone]], [[pregnenolone]], [[progesterone]], and other steroid products.<ref>{{cite journal |vauthors=Marker RE, Krueger J |date=1940 |title=Sterols. CXII. Sapogenins. XLI. The Preparation of Trillin and its Conversion to Progesterone |journal=[[Journal of the American Chemical Society]] |volume=62 |issue=12 |pages=3349–3350 |doi=10.1021/ja01869a023 |bibcode=1940JAChS..62.3349M }}</ref> Such preparations were used in early [[combined oral contraceptive pill]]s.<ref>{{cite journal |last=Djerassi |first=C. |date=December 1992 |title=Steroid Research at Syntex: "The Pill" and Cortisone |journal=[[Steroids (journal)|Steroids]] |volume=57 |issue=12 |pages=631–641 |doi=10.1016/0039-128X(92)90016-3 |pmid=1481227 |s2cid=5933910|doi-access=free }}</ref> The unmodified steroid has [[estrogenic]] activity.<ref>{{cite journal |vauthors=Liu MJ, Wang Z, Ju Y, Wong RN, Wu QY |date=2005 |title=Diosgenin induces cell cycle arrest and apoptosis in human leukemia K562 cells with the disruption of Ca<sup>2+</sup> homeostasis |journal=[[Cancer Chemotherapy and Pharmacology]] |volume=55 |issue=1 |pages=79–90 |doi=10.1007/s00280-004-0849-3 |pmid=15372201 |s2cid=11779821 }}</ref>

== In culture ==
[[File:Ashanti Yam Ceremony 1817.jpg|thumb|upright=1.25|1817 painting of [[Ashanti yam ceremony]], [[Ghana]]]]

Historical records in West Africa and of African yams in Europe date back to the 16th century. Yams were taken to the Americas through precolonial Portuguese and Spanish on the borders of Brazil and Guyana, followed by a dispersion through the Caribbean.<ref>{{cite web |url=http://www.fao.org/docrep/t0207e/T0207E01.htm |title=Roots, Tubers, Plantains and Bananas in Human Nutrition |at=Acknowledgments, preface, introduction, origins, and distribution |publisher=United Nations [[Food and Agriculture Organization]] }}</ref>

Yams are used in [[Papua New Guinea]], where they are called ''kaukau''. Their cultivation and harvesting is accompanied by complex rituals and taboos. The coming of the yams (one of the numerous versions from [[Maré]]) is described in Pene Nengone ([[Loyalty Islands]] of [[New Caledonia]]).{{Citation needed|date=November 2021}}

=== Nigeria and Ghana ===
A yam festival is usually held in the beginning of August at the end of the [[rainy season]]. People offer yams to [[Odinala|gods and ancestors]] first, before distributing them to the villagers.{{Citation needed|date=April 2025}}

The New Yam Festival celebrates the main agricultural crop of the [[Igbo people|Igbos]], [[Idoma people|Idomas]], and [[Tiv people|Tivs]]. The New Yam Festival, known as ''Orureshi'' in Owukpa in Idoma west and ''Ima-Ji'', ''Iri-Ji'' or ''Iwa Ji'' in [[Igboland|Igbo land]], is a celebration depicting the prominence of yam in social and cultural life.{{Citation needed|date=April 2025}}

The Igbo people accord special respect to yam to the extent that no one eats the newly harvested yam until the New Yam celebrations or feast is marked. It is called Iri ji ọhụrụ.{{Citation needed|date=April 2025}}

{{Clear}}

== References ==
{{Reflist}}

== External links ==
{{Commons category|Yam|Yams}}
{{Wiktionary| yam}}
{{NIE Poster|Yam}}
* {{Cookbook-inline|Yam}}
* {{cite web |url=http://www.iita.org/research/our-research-themes/improving-crops/yam-crop-improvement/ |website=[[International Institute for Tropical Agriculture]]|title=Yam crop improvement}}

{{Bioenergy}}

[[Category:Yams (vegetable)| ]]
[[Category:Crops]]
[[Category:Crops originating from Africa]]
[[Category:Dioscorea]]
[[Category:Flora of Jamaica]]
[[Category:Igbo cuisine]]
[[Category:Plant dyes]]
[[Category:Root vegetables]]
[[Category:Staple foods]]
[[Category:Tropical agriculture]]
[[Category:Tubers]]
[[Category:Yoruba cuisine]]