Morning Glories Morning Glory - family Convolvulaceae
Yam - family Dioscoreaceae

Arrrrgg! How could I do this?   I have lumped on the same page two plant families that differ at the Top Clade Level. Yams are monocots and Morning Glorys are astrid eudicots - you just can't get any farther apart and still be flowering plants. Well, they look so similar (twining vines with tuberous roots and heart shaped leaves) and are used so similarly, they are commonly confused. Putting them in one place helps sort them out. Photo © i0133.





Morning Glory

The Morning Glory family (Convolvulaceae) are eudicots found worldwide in all climates, but the culinary ones all belong to the genus Ipomoea, which inhabits only tropical and subtropical regions. A few of the other genera produce seeds which are sometimes ingested but not for the purpose of nutrition.

Sweet Potatoes & U.S. "Yams"

Sweet potato vines are members of the Morning Glory family native to Central America and the Caribbean. They are unrelated to true potatoes which are Nightshades. They produce an edible "storage root" which is non-toxic and under proper "curing" conditions converts part of its starches to sugars making it sweet.

The United States grows less than 1% of worldwide production. The rest is grown in Asia and Africa, with China accounting for more than 80% of world production.

Sweet potatoes are further evidence of contact between South America and the Pacific Islands in pre-Colombian times. The Quechua (Peru) name for sweet potatoes is Kamar. The name Kamara and similar are common in Polynesia and New Zealand. It is certain the Pacific Islands had sweet potatoes before European contact, and that they couldn't have floated that far on their own.

Sweet Potato, White   -   [Boniatos (Caribbean); C. Ipomoea batatas]
White Sweet Potato

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"   -   [Red Sweet Potato; C. Ipomoea batatas]
Red Sweet Potato

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   -   [Japanese Sweet Potato, Satsumaimo; C. Ipomoea batatas]
Japanese Purple Skinned 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   -   [Hawaiian Sweet Potato; Uala (Hawaii); C. Ipomoea batatas \ cv. Ayamurasaki]
Okinwan Purple 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   -   [#94622 C. Ipomoea batatas]
Stokes Purple Sweet Potato

These are a patented variety of Stokes Foods, organically grown under contract in California and North Carolina. Chunks will simmer tender in 10 minutes, but start to break up at 25 minutes. These are moderately sweet sweet potatoes. They ares sold through Whole Foods Market and other Yuppie oriented outlets, 2017 US $2.49 / pound. The purple color comes from anthocyanin flavonoids, which have antioxidant properties, but how well these survive digestion is debatable.

Other Sweet Potatoes   -   [Goguma (Korea); Kumara (New Zealand); Batata (most Spanish and Portuguese, from Taino); Camote, Kamote (Philippine, from Nahuatl); Boniato (Spain, Uruguay); Patata americana (Italy); Shakarkand (india); Satsuma-imo (Japan); C. Ipomoea batatas]
Purple Sweet Potato

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 Stems & Leaves   -   [ C. Ipomoea batatas]
Sweet Potato Stems

Young leaves and growing tips (stems) of the vines of sweet potatoes are quite edible. These greens are eaten in many parts of Asia, particularly Taiwan and the Philippines, and especially in Africa. For some reason Koreans use only stems and not the leaves. 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   -   [230; Dangmyeon (Korea)]
skein of thin 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.

Water Spinach   -   [Swamp Cabbage; Ong Choy - variously spelled (Cantonese); Pak Hung, Pak Bung (Thai); Kang Kong (Malay, Filipino); Kang Kung, Rau Muong (Vietnam); Toongsin Tsai (Mandarin); Chinese Watercress, Water Convolvulus, Water Morning-glory; Ipomoea aquatica also Ipomoea raptans (not common)]
Stems with Leaves

This semi-aquatic plant is a controlled substance within the USA. Importing plants or seeds and/or growing plants without a permit are all illegal - see USDA Plant Profile. Growing it or even transporting it is totally illegal in some states.

Here in California it is a quarantined crop but may be transported without a permit within the state. Enough growers have permits it is in good supply, and that's a good thing because if it wasn't our large Asian population might try sneaking it into our waterways like they did with snakehead fish.

There are several varieties of this vegetable, including a long leafed variety that can be grown in damp soil (Ching Quat) and a wider leafed variety that requires free water (Pak Quat). The wider leaf variety is preferred in Asia but is rarely available here, probably to keep the growing areas farther from our waterways. The photo specimens are about 19 inches long. Details and Cooking.


These tropical vines, native to Africa and Asia, are quite unrelated to the Sweet Potato vines and are in the same clade as lilies (monocots). They produce root tubers which are generally toxic, some less so, some more so, but it's best to avoid eating most of them raw. Some require tedious pounding and leaching to make them edible but these are not sold as vegetables in the USA. The varieties sold here just require a little cooking for detox.

Yam (True)   -   [boniato (Spanish), nyami (Africa); ñame (Panama); D. Dioscorea batatas and similar]

Yams are grown in Africa, the Caribbean and Latin America, but not in the U.S. except a few in Florida. 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.

New Zealand Yam   -   [oca, oka (Andean), Oxalis tuberosa]
Neither a yam nor a sweet potato but a completely unrelated tuber from the Andean area of South America. See Oxalis Family.

Nagaimo   -   [Nagaimo, Yamaimo (Japan); Glutinous Yam, Cinnamon vine, Japanese Mountain Yam, Chinese Yam; Ma (Korea); Shan yao, Huai shan, Huai shan yao (China); Dioscorea opposita]

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   -   [Violet Yam, Water Yam, Ube, Halaya (Filipino); Ratalu (India); Uhi (Hawaii); Beniimo (Okinawa);Dioscorea alata]
Purple 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.   Photo by Obsidian Soul distributed under license Creative Commons Attribution-ShareAlike v3.0 Unported.

Yampi   -   [Cushcush, Indian yam, napi; Yampi, Yampie (Jamaica); Maona (Peru); Mapuey (Puerto Rico); Aja (Cuba); Cara doce (Brazil); Dioscorea trifida]

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.

mg_mglory 2006   -
©Andrew Grygus - - Photos on this page not otherwise credited © cg1 - Linking to and non-commercial use of this page permitted