Morning Glory - family Convolvulaceae
Yam - family Dioscoreaceae

Sweet Potato, White

These are the standard grocery store white sweet potato. Sweet potatoes (red or white) are not particularly sweet at harvest but are "cured" at 85°F for 4 to 7 days during which some of the starch is converted to sugar. Pictured are 1/2 pound potatoes.

Select firm sweet potatoes with no soft spots. Do not refrigerate Sweet Potatoes. Temperatures below 55°F will make them hard and ruin the flavor. They should be stored loose (not in plastic) and kept away from sunlight. Stored at 55°F to 60°F and 90% humidity they'll keep for several months but in a normal household environment they should be used within a couple of weeks.

U.S. "Yam"

This is not actually a yam but a sweet potato variety with red skin and orange flesh. The term "Yam" was adopted from the African "nyami", the name used for sweet potatoes by Southern slaves. This was to differentiate it from the white sweet potato in commerce. Unlike True Yams they have smooth skin as other sweet potatoes do.

Pictured are a whole 2 pound and a cut piece from a 1/2 pound sweet potato. This "Yam" has orange flesh that is moister and sweeter than that of the White Sweet Potato, but all other characteristics are pretty much the same.

Murasaki Sweet Potato

In North America, this sweet potato is currently sold mostly through Yuppie oriented outlets like Trader Joes. They can be cooked by any method used for regular North American sweet potatoes, but are a bit drier, almost like a russet potato. They are quite sweet, with a pleasant nutty flavor. The raw flesh is just slightly yellow, but becomes more intensely yellow with cooking. They hold up fairly well to wet cooking, if it's not too long. The photo specimens were purchased from Trader Joe's at 2017 US $1.33 / pound. Average weight was 9 ounces and 2-3/4 inches diameter, varying from almost spherical to short elongated.

Okinawan Sweet Potato

These light beige skinned sweet potatoes were carried from the American tropics to the Philippines and China by the Spanish, reaching Okinawa around 1600. They are now grown on the Japanese main islands, but still considered "Okinawan", with the Murasaki considered "Japanese". They are quite available in Asian markets here in Los Angeles, always confusingly labeled "Purple Yam". Real Purple Yams are not currently much available in North America. The purple color comes from anthocyanin flavonoids, which have antioxidant properties, but how well these survive digestion is debatable.   Details and Cooking.

Stokes Purple Sweet Potato

These are a patented variety of Stokes Foods, organically grown under contract in California and North Carolina. It is unknown where they came from, but sweet potato experts are pretty sure they originated from Asia. Chunks will simmer tender in 10 minutes, but start to break up at 25 minutes. These are moderately sweet sweet potatoes, and their flesh is a little drier than white sweet potatoes. They ares sold through Whole Foods Market and other Yuppie oriented outlets, The photo specimens cost 2017 US $2.49 / pound. The purple color comes from anthocyanin flavonoids, which have antioxidant properties, but how well these survive digestion is debatable.

Red Skinned Purple Sweet Potato

These resemble the Stokes Purple in many ways, but would have been clearly labeled if that's what they were. They probably originated from wherever the Stokes originated from. The photo specimens were purchased from a large Asian market in Los Angeles (San Gabriel) for 2019 US $1.29 / pound. The larger of them was 8-1/4 inches long, 3-1/4 inches diameter and wighed 1-3/4 pounds.

Other Sweet Potatoes

Purple sweet potatoes are grown in much of Asia, including New Zealand, Australia and Japan. Both the skin and flesh are purple, and the color survives cooking. Other colors are also grown through the region.

Yellow fleshed sweet potatoes with red skins are known in North America as "Korean sweet potatoes", but are also grown in other parts of Asia, including Japan and New Zealand. The yellow color is quite bright in Korea and Japan, but very pale in Indonesia. This is the most common sweet potato in China. Yellow sweet potatoes are grown in Australia, but most grown there are the American orange fleshed variety.

New Zealand grows three varieties. A red skinned sweet potato with white flesh streaked with purple is most common, but the yellow fleshed and American orange fleshed are also grown.   Photo by Earth100 distributed under license Creative Commons Attribution-ShareAlike v3.0 Unported.

Sweet Potato Leaves (Yam Leaves)

[Boniatos (Caribbean); Talbos ng kamote (Philippines); Rau Lang (Viet); Di gua ye (Taiwan); Hong shu ye, Fan shu ye (China); C. Ipomoea batatas]

What is sold as "Yam Leaves" in the markets is invariably Sweet Potato Leaves, because many real Yams have somewhat toxic leaves. Sweet Potato leaves are a popular green in much of the world, and they can be used as a substitute for the closely related Water Spinach, which is illegal in much of North America.   Details and Cooking.

Sweet Potato Stems

Use of Sweet Potato stems without the leaves is a Korean specialty. Both fresh stems and dried stems are used for banchan (small side dishes). The leaves are discarded and the stems are peeled, which is tedious. In Korea they are also sold pre-peeled in bags of water. The season for fresh stems is short, so stems are used dried the rest of the year. While cooked similarly, the flavors and textures are significantly different. This is not the only plant where the leaves are eaten elsewhere but only the stems in Korea.   Details and Cooking.

Sweet Potato Starch Noodles

Instructions for these are fairly clear. Boil for 6 to 8 minutes (I say more like 8 to 10 minutes), drain and refresh with cold water, then mix with salad, cold dish, appetizer or as ingredient in hot pot. These are essential to the famous Korean dish Japchae. The photo specimens were made in China, 0.06 diameter by 22 inches folded length. Ingred: sweet potato starch, sulfur dioxide, water. They cook to a firm jelly consistency. Flavor and texture are pleasant and these noodles are much more durable in recipes than bean starch noodles.

Yam, White / Yellow

True Yams are grown in Africa, Southeast Asia, the Caribbean and Latin America, but are only beginning to take root in North America. Unlike sweet potatoes they have a rough scaly skin, and can grow to as much as 150 pounds, though they are generally marketed at only a few pounds. Both White and Yellow varieties are native to Africa, but now grown in the Tropics worldwide.   Details and Cooking.

Yam Leaves

What is sold in the market as "Yam Leaves" are actually Sweet Potato leaves. Real Yam Leaves are eaten in some districts of India and Southeast Asia where they have suitable varieties, but most leaves of real Yams are toxic to some extent.

New Zealand Yam

Nagaimo

Native to Southern China this yam has been cultivated in Japan from very early times. Known in the U.S. mainly as an invasive weed, this vine with arrowhead shaped leaves grows large tubers below ground and small tubers above ground. It spreads mainly by dropping these small "air potatoes" and rarely flowers.

Nagaimo is roughly cylindrical and may be up to three feet long, but the photo specimen was 24 inches long, 2-7/8 inches diameter and weighed 3-1/4 pounds. The skin is tan and the flesh is white and, unlike other yams, sticky and more than a bit slimy. The two Japanese names, nagaimo and yamaimo (shorter, thicker), are applied depending on the root shape.   Details and Cooking.

Purple Yam / Water Yam

Native to Southeast Asia, there are many cultivars of this yam, varying from deep purple to white. Intensely purple varieties are very popular through South and Southeast Asia, while most grown in Africa are white. These are the most common yam in Africa, but are little available in North American markets, even in Los Angeles with our large Philippine population. They are listed as noxious weeds in a few southeastern states, particularly Florida. The purple color comes from anthocyanin flavonoids, which have antioxidant properties, but how well these survive digestion is debatable.   Details and Cooking.

Yampi

Native to the Caribbean and tropical Central America this yam is grown for its starchy roots and used similarly to Cassava. It contains the bitter toxic alkaloid discorene which is eliminated by cooking. The cut ends of the photo specimens were dipped in wax to prevent drying out and shriveling. The largest of the photo specimens was 11 inches long, 2-1/2 inches diameter and weighed 1 pound.

Raw yampi are very mucilaginous but this goes away when cooked. Cooked the texture and flavor are pleasant and much like a waxy potato but more tender and crumbly and noticeably sweeter. While yampi is a very fine edible, it is overshadowed in its growing region by manioc (cassava) which produces a higher yield and is more durable in storage.