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 moncots 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) is 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.

Sweet Potato, White   -   [kumara (New Zealand - Maori); 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.

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); 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 two or 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.

Violet Yam   -   [Purple Yam; Ube, Halaya (Filipino); Ratalu (India); Uhi (Hawaii); Dioscorea alata]
Violet Yam

This violet fleshed yam, now easily available in Southern California in Asian markets, is native to East Asia. It is very sweet and used mainly for deserts, particularly in the Philippines. In India it is also used for deserts but also appears in mixed vegetable dishes. Cooked, its purple color darkens and intensifies.

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