Delaware Wildflowers • Misc

Potatoes, sweet potatoes, and yams
A field guide to market tubers
A few weeks ago we got some of these beautiful "purple yams" at the Newark Farmers Market. A little Googling told us that purple yams are called ube in the Philippines, and are used in desserts.

We found a recipe and made some cupcakes. We were going to share some, and it occurred to me that someone might ask if those purple yams were really yams, or were they sweet potatoes, and what's the difference anyway.

I determined that these are actually purple sweet potatoes, murasaki imo in Japanese, also called Okinawa sweet potatoes — not ube. (The cupcakes were quite tasty anyway!)

I'm not going to tell anyone what to call their food. "Yam" and "sweet potato" are pretty much interchangeable in the U.S., but if you want to make a distinction based on botany, read on. There are many "yam vs. sweet potato" explanations online, but I didn't find any that seemed completely adequate. So here's mine, with potatoes thrown in for good measure.

Common namePotato
Irish potato
White potato
Sweet potato
In the marketThey look like potatoes, they're called potatoes. No confusion here.They're just as likely to be called yams as sweet potatoes, but whatever they're called, they look like sweet potatoes, and that's what they are.They don't look like potatoes or sweet potatoes. At the Newark Farmers Market (the only place I've seen them for sale) the signs above them say "name", but some have stickers that say "yam".
Scientific nameSolanum tuberosumIpopmoea batatasDioscorea spp.
(see Wikipedia for species)
(Nightshade family)
(Morning-glory family)
(Yam family)
Edible partStem tuberRoot tuberRoot tuber
Shape & sizeRounded; mostly under a pound.Tapered at both ends; often over a pound, especially those called yams.Cylindrical, or irregularly lobed; mostly over a pound, up to over 100 pounds. The yam in the photo above is 10" long and 2.5 pounds.
SkinSmooth or slightly rough, in colors from almost white to purple, but typically brown; edible.Not as smooth as potato skin, in colors from tan (most common) to purple; edible, but most prefer them peeled.Brown and rough (some say scaly or bark-like); inedible.
FleshVaries in color, but is typically white.White to purple, but is typically pale yellow or orange.White, yellow, or pale purple.
OriginSouthern Peru
Domesticated 7-10,000 years ago
Central or South America
Domesticated at least 5,000 years ago
Africa and Asia
Cultivated 10,000 years ago
  • Vitamin C
  • Fiber
  • Carbohydrate
  • Iron
  • Vitamin A
  • Vitamin C
  • Fiber
  • Carbohydrate
  • Vitamin C
  • Fiber
  • Carbohydrate
  • Creamer, red (4723), white (4724)
  • Long, white (4726)
  • Potato, purple (3128), red (4073), white (4083), yellow (4727)
  • Russet (4072, 4725)
  • retailer assigned (4728-4733)
  • Boniato / Sweet Potato (4546)
  • Sweet Potato / Kumara, golden (4816), white (4091); red / orangy, white flesh, small (3333), large (3334); red flesh, small (4074), large (4817)
  • retailer assigned (3288)
  • Yam, white (3276), yellow (3275)
  • retailer assigned (4818)
Delaware wildflowersSeveral Solanum species can be found in Delaware. As far as I know, none are edible.Several Ipomoea species can be found in Delaware. I. pandurata is reported to have edible roots!Two Dioscorea species can be found in Delaware. D. polystachya (D. batatas, D. oppositifolia) is reportedly edible.

More links & references:
This is interesting, the author is really trying to get it right, and gets it wrong anyway. Everything in the photo of tubers on a black tray is a sweet potato, except the one at bottom right.
This is where I got the Japanese common names.
This is what happened to the yam in the photo above. Delicious!

Copyright David G. Smith

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