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DIOSCOREA alata

Image of Dioscorea alata

Forest & Kim Starr

Family

Dioscoreaceae

Botanical Name

DIOSCOREA alata

Plant Common Name

Purple Sweet Potato, Purple Yam, Ubi, Uhi, Water Yam, White Yam, Winged Yam

General Description

Of all the cultivated yams, this is one of the most extensively grown. The water yam is a large, vigorous tender perennial vine that produces starchy, edible, bulbous tubers that may be white or purple fleshed. It is a major crop in the tropics and has become naturalized in many parts of the world, including the southern United States. This species is thought to have originated from Eastern Asia. Hundreds of cultivated varieties exist that vary in tuber consistency, color and size.

Water yam has long, twining stems of green or reddish purple with distinctive winged ridges. Its deep green, heart-shaped leaves are smooth and have a lustrous sheen. Unusual, tuberous, brown, aerial bulbils shaped like half moons form along the base of the leaves. The bulbils will root to form a whole new plant and are dispersed by water. Dioscorea is a dioecious genus, which means each plant has either male or female flowers, never both. The small, greenish ivory male flowers are borne on long panicles and the small female flowers short ones. Female plants produce three parted capsule fruits that contain winged seeds that are dispersed by the wind.

The edible tubers of this vine are typically produced in bunches and can become massive. Some have been recorded as weighing as much as 100 to 150 pounds (~45 to 70 kg). They are typically white fleshed and have a pleasing starchy flavor and floury texture. Purple fleshed selections are common too—especially in East Asia—as are pink and yellow fleshed varieties. Water yams are considered the most potato-like of all the edible Dioscorea. They are usually harvested at the end of the rainy season in tropical and subtropical areas or in late summer in more temperate climes.

Yams grow best in full to partial sun and fertile, friable soil. In frost-free zones they go dormant after the rainy season for a period of two to three months. In more temperate zones dormancy occurs in winter. The vines can become quite invasive and will cover and overpower surrounding plants entirely if not harvested regularly. They rarely spread by seed but spread quickly and effectively by their bulbils and tubers. In many countries this species is listed as a noxious weed, in fact it is on the Florida state list if noxious weeds. To learn more about the invasive nature of Dioscorea alata visit the Global Compendium of Weeds page on the species: http://www.hear.org/gcw/species/dioscorea_alata/

Yams are very versatile and are eaten mashed, roasted, stewed fried or pounded into flour. They can be added to savory or sweet dishes but most often accompany meat or vegetables, like pumpkin and corn.

Characteristics

  • AHS Heat Zone

    10 - 1

  • USDA Hardiness Zone

    6 - 10

  • Plant Type

    Vegetable

  • Sun Exposure

    Full Sun, Partial Sun

  • Height

    20'-30' / 6.1m - 9.1m

  • Bloom Time

    Summer

  • Native To

    Asia

Growing Conditions

  • Soil pH

    Acidic, Neutral, Alkaline

  • Soil Drainage

    Average

  • Soil type

    Clay, Loam

  • Growth Rate

    Very Fast

  • Water Requirements

    Average Water

  • Habit

    Vining/Climbing

  • Seasonal Interest

    Summer, Fall

Ornamental Features

  • Flower Interest

    Insignificant

  • Flower Color

    Yellow Green, Ivory

  • Fruit Color

    Brown, Sandy Brown

  • Foliage Color (Spring)

    Green

  • Foliage Color (Summer)

    Green

  • Foliage Color (Fall)

    Green

  • Fragrant Flowers

    No

  • Fragrant Fruit

    No

  • Fragrant Foliage

    No

  • Bark or Stem Fragrant

    No

  • Repeat Bloomer

    Yes

  • Showy Fruit

    No

  • Edible Fruit

    No

  • Showy Foliage

    Yes

  • Foliage Texture

    Coarse

  • Foliage Sheen

    Glossy

  • Evergreen

    No

  • Showy Bark

    No

Special Characteristics

  • Usage

    Edible, Herb / Vegetable, Tropical, Vine

  • Sharp or Has Thorns

    No

  • Invasive

    Yes

  • Self-Sowing

    No