1276 Dioscorea alataCommon Names: purple yam,ube,winged yam,white yam,water yam,greater yam Family: Dioscoraceae (yam Family)
Purple yam is a vigorous climbing herbaceous (not woody) vine that twines around, through and over its supporting structure. Purple yam vines lack any of the specialized structures that enable various other vines to climb, such as tendrils, root hairs, adhesive pads, or hooklike thorns. Purple yam vines twine clockwise and the winged stems can get up to 30 ft (9 m) or more in length. The leaves are opposite, 6-8 in (15-20 cm) long, heart shaped, and green or purple in color. The fast growing vines with their large heart shaped leaves are quite attractive, and they can quickly grow into the tops of tall trees, even smothering them. Grayish brown potato-like bulbils (aka, aerial tubers), up to 4 in (10 cm) long, are produced abundantly along the vines. Purple yams are dioecious, with male flowers borne in long hanging clusters up to a foot (30 cm) in length, and female flowers in smaller erect spikes. The fruit is a capsule that opens when ripe to release winged seeds.
The tubers of purple yam can get up to 8 ft (2.4 m) long and weigh as much as 100 lbs (45 kg)! The skin and the insides can be white or bright lavender, depending on variety. When cut into, they are slimy, like sliced okra.
Dioscorea alata probably originated in Southeast Asia, but a wild, uncultivated purple yam is not known to exist anywhere. Purple yam is, however, widely cultivated in tropical regions in both hemispheres, is a staple in the Philippines, and is just coming into favor in the southeastern U.S. and Gulf Coast. It is extensively cultivated in the West Indies and Central America. Purple yam has escaped cultivation and become a noxious invasive weed in many parts of the tropics and subtropics, especially in Florida and Louisiana.
Light: Purple yam does best when it is growing in full sun, but partial shade is okay, too. Moisture: Keep the soil just moist (not waterlogged), and provide supplemental irrigation during dry periods. Purple yams need a lot of moisture during growth. In the tropics, purple yams undergo a 2-3 month period of dormancy at the end of the rainy season. Hardiness: USDA Zones 8 - 11 . The foliage of purple yam will not survive freezing temperatures, but the tubers may survive until spring and then resprout. These yams need 6-12 months of warm soil to produce a respectable crop of tubers. Yams grown in subtropical and temperate climates (such as the southeastern US Gulf Coast) rarely produce flowers or fruits. Propagation: Propagate purple yam, and most other yams as well, by dividing and replanting the tubers, or by rooting the young shoots that arise from a tuber. You can cut the tubers before planting as you would a potato; just be sure to leave two or three buds on each piece. Set them out three weeks after the last danger of frost. Be sure to supply support for the rampant vines to climb on. The aerial tubers also can be planted.
Purple yams are cultivated extensively for their edible tubers in southeast Asia and West Africa, where they are an important source of starchy carbohydrates. They are always cooked before eating. In many African cuisines, yams are peeled, boiled and mashed, and then dried and ground into a powder that can be used like flour. In developed countries, purple yam is most often used in deserts, including ice cream, cakes, cookies and other pastries. It is used to flavor milk and tea. Perhaps purple yam’s most well known use is in the traditional Philippine dessert, ube halaya, a jelly-like concoction that includes purple yam, coconut milk, sugar and vanilla. Ube halaya is lately trending in restaurants and kitchens in the United States. Here at Floridata, we plan on trying purple yam in some savory recipes such as baking, boiling, roasting, sautéing in olive oil, and frying. Stay tuned!
Yams store poorly, so don’t dig them up until ready to use. Tubers are usually harvested at the end of a single growing season. Left in the ground, tubers will continue to increase in size in subsequent years, eventually reaching humongous proportions.
Yams contain the steroid diosgenin, which is a used in the manufacture of birth-control pills. Research suggests also that purple yams contain compounds with antifungal properties.
Where not hardy, purple yam, especially any variety with purple leaves, is suitably attractive as a hanging foliage container plant or summertime ornamental on a trellis.
Americans sometimes refer to sweet potatoes (Ipomoea batatas), especially the long thin orange fleshed ones, as yams, but sweet potatoes are dicots in the morning glory family (Convolvulaceae), and not even remotely related to yams. In fact, yams are monocots in their own family, the Dioscoraceae, and more closely related to grasses and palms. Sweet potatoes may be orange, white or even purple on the inside, whereas yams are typically either white or purple. Yams have a scaly and rough barklike outer skin, whereas sweet potatoes have a smooth, thin skin. Sweet potatoes are cylindrical with tapered ends whereas yams tend to be more rounded. Sweet potatoes are rarely longer than about a foot (30 cm), and seldom heavier than about a pound (.45 kg), whereas yams can get more than 5 ft (1.5 m) long and weigh over a hundred pounds (45 kg). Yams are drier and starchier than sweet potatoes.
There are more than 600 species of true yams (genus Dioscorea), all twining vines with tuberous roots, and most restricted to tropical or subtropical climates.
Purple yam (Dioscorea alata) is listed as a Category I invasive species on the Florida Exotic Pest Plant Council’s List of Invasive Plant Species. It is considered an invasive pest by the State of Florida, although its cultivation is not prohibited. Purple yam is closely related to air potato (Dioscorea bulbifera), which also is a serious pest in Florida. Floridata believes that neither species should be cultivated in Florida. Purple yam is known to disrupt natural plant communities, especially coastal hammocks in southern Florida. Fairly large populations occur in northern Florida as well. Stands of purple yam have been known to completely cover and kill native trees and shrubs.
To prevent yams from spreading, always harvest all of the tubers at the end of the growing season and replant each year. Also, remove and destroy the aerial tubers that grow on the vines.
Most yams are bitter and poisonous until cooked, although many of the modern edible cultivars are probably not.
Steve Christman 12/26/16