Q: When is a yam not a yam?

A: When it’s a sweet potato or a taro!

I have recently discovered that I have been using imprecise names, and probably confused some of you in other parts of the world where different words are used.

For example, I learnt from reading this that in America, what are called ‘yams’ are really varieties of sweet potato which have a moist texture.

In contrast, I have been referring to taro as ‘yam’, basically equating anything we call in Chinese yu4tou3 芋頭 with ‘yam’. While one could put it down to a combination of my poor plant-recognition skills and half-baked linguistic ability, I’m not the only person who equates yu4tou3 芋頭 and ‘yam'; so does this bilingual food blog from Singapore. And after all, we call steamed 芋頭糕 yu4tou2gao1 [Mandarin]/ wu tao gou [Cantonese], ‘Yam Cake’ (and I made some Shredded Yam Cake 芋絲餅). Lily’s Wai Sek Hong, a Malaysian writing from America helps to unravel the puzzle with this explanation:

In Malaysia, ‘Woo Tau’ in Cantonese is called YAM but it is TARO here in the States and yam is sweet potato.

Trying to look for bilingual dictionary definitions can be hugely confusing too. On the Chinese-language internet, the most common list of food words provides this translation:

yam — shan1yu4 — 山芋
taro — yu4tou2 — 芋头

On the other hand, my US-produced dictionary follows the American usage:

sweet potato – shan1yu4 — 山芋
yam — shu3 — 薯

[How, er, not helpful: ma3ling2shu3 馬鈴 = potato; mu4shu3 木薯 = tapioca; and to Southeast Asian Chinese, fan1shu3= sweet potato, following Cantonese usage, cf. China, where sweet potatoes are called di4gua1 地瓜].

But back to 山芋 (shan1yu4 in Mandarin). When pronounced in Japanese, it’s yamaimo — that very special ingredient needed to make okonomiyaki! Yamaimo is usually translated into English as ‘mountain yam’.

To get to the root (no pun intended!) of the issue, we’ll have to look at the botanical names:
yam – genus: Dioscorea
taro — genus: Colocasia
sweet potato — genus: Ipomoea

While the Colocasia genus comprises only six to eight different types of flowering plants, there are 600 varieties of Dioscorea, of which the edible ones are known as yams. The genus Ipomoea also has over 500 species, some of which we commonly recognise as the morning glory flower, and others in the form of edible tubers, i.e. sweet potatoes.

Within the Dioscorea family, the species of edible tubers we call yams come in a mind-boggling diversity. From the long, cream-coloured, stick-like Chinese/Japanese mountain yam 山芋, to huge, dark brown, ugly, knobly lumps. But don’t be put off by the external appearance, a yam that looked like a piece of elephant dung on the outside, turned out like this:

Purple Yam

Aren’t the variegated colours beautiful? I have no idea what the correct name for this kind of yam is, but here’s a photo of the whole tuber from a Japanese blog that refers to it as murasaki yamaimo 紫山芋, ‘purple yam’. Unfortunately, to me this was rather bland, taste-wise, and too dry and powdery in texture for my liking (think of powdery potatoes, the kind used for baked potatoes, as compared to the smooth, waxy kind used for roast potatoes).

Previously, I was also wasthe misconception that yams are always purple and anything purple is a yam. After all, yam-flavoured ice cream is always purple isn’t it? Of course that’s just food colouring, but it is based on the perception that yams are purple. It was only when I bought purple sweet potatoes for these two-coloured sweet potato balls and this purple soup, did I realise that yams do not have a monopoly on this rich colour.

Here’s a photo from Nakashima Farms, a Californian-Japanese producer of sweet potatoes, showing the four varieties they sell. I was amazed and impressed by the different coloured flesh (yikes! no wonder the sweet potato I bought didn’t look like the one in the recipe book!).

Sweet Potatoes Colours

The purple sweet potato shown here is known as the Okinawan variety from Japan. I’m not sure whether the ones I got for the two-coloured sweet potato balls and purple soup were also the Okinawan variety, but they were labelled as originating from Thailand (purchased in Sheng Siong).

Right now, my favourite kind is the Japanese variety, satsumaimo さつまいも, shown on the extreme left (or see photo here). It’s purple on the outside but not on the inside ^_^. The pale yellow flesh is sweet and very smooth. In contrast, the typical local sweet potatoes, which are orange both outside and within, I’ve found are extremely fibrous, making the texture unpleasant when eating them whole, and necessitating a lot of sieving if you want to use them in recipes like the two-coloured sweet potato balls.

Satsumaimo from Japan can be rather pricey, so an alternative is are the ‘Japanese sweet potatoes’ grown in Vietnam. They are usually very small – just the right size for a snack bento – and are often sold in bags at the supermarket. The other day, I bought a full-sized satsumaimo for the first time, and found it much more satisfying than the tiny Vietnamese ones.

Now that we’ve got yam, taro and sweet potato sorted out, what about the difference between roots, tubers, corms and rhizomes? … Maybe another time, my head is spinning already :P.

If you’re dying to pursue this line of inquiry further, do have a look at this page from S. J. Kays at the University of Georgia on Cultivated Edible Root, Tuber, Rhizome, Bulb and Corm Crops of the World, which includes a list of the most commonly cultivated root and tuber crops with their names in sixteen different languages (and botanical name, of course), photographs and even bibliographies of the latest scientific publications on each variety. From a more culinary perspective, the Cook’s Thesaurus on ‘Sweet Potatoes & Yams‘ as well as on ‘Tubers & Corms‘ are a good reference.

P.S. Maybe you’ve guessed already, my favourite rhizome is wasabi (^_*)!

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2 Responses

  1. The Purple Yam shown above in 1st Pic, is called “Kan” or “Rataloo” in India. Most of the people from the State of Gujarat (in India) have this yam when they are fasting…

  2. Thank you for this usefull information, I`m from Germany and got really confused about all yam kinds and names.
    I have few sites about ingredients on my blog, can I use the information from here?Please?(not pics, only info :-))
    I also have a post about japanese wagashi flours, maybe this would be interesting for you.I would like to know the chinese flours more exactly.
    My blog is in german/english.

    Your blog is great, I like you post some “katastrophes”, this is sweet. ;-)

    Regards, Amato

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