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]
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]
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.
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 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
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. The Japanese consider the yellow "Japanese" and the Purple
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
Attribution-ShareAlike v3.0 Unported.
Sweet Potato Stems & Leaves
- [ C. Ipomoea batatas]
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)]
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
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)]
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
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
[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);
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.
[Cushcush, Indian yam, napi; Yampi, Yampie (Jamaica); Maona (Peru);
Mapuey (Puerto Rico); Aja (Cuba); Cara doce (Brazil);
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.