Dioscoreaceae, the Yam Family
Air potato is an aggressive, herbaceous vine that can attain lengths of 65 feet in a single growing season. Underground tubers may be present or absent. The slender stems twine to the left (counter-clockwise) and are round to slightly angled in cross section. Leaf arrangement is consistently alternate. The thin textured, glabrous (hairless) leaves, which measure from 2 to 10 inches long, are cordate (heart-shaped) with broadly rounded basal lobes, elongated tips and entire margins. The venation is conspicuous on the upper leaf surface, with arching primary veins all originating from the sinus at the base of the blade and secondary veins running between adjacent pairs of primary veins, giving the leaf surface a bullate (puckered or quilted) appearance. The petioles (leaf stalks) are almost as long as the leaf blades, have a flattened upper surface and flare out to form ruffled wings at the junction with the blade.
Air potato is dioecious (with carpellate (female) and staminate (male) flowers borne on separate plants), and only carpellate plants have been observed in Florida. The carpellate inflorescences are spikes to 16 inches long that may be borne singly or in fascicles of up to six in the leaf axils. Each carpellate inflorescence bears up to 50 tiny greenish-white flowers. Flower production is not common in Florida air potato plants, but is most likely to occur at the end of the growing season (late summer through early winter). Since staminate plants have not been documented in Florida, there is no sexual reproduction and seed production. Instead, plants reproduce asexually by means of bulbils (aerial tubers). One to four bulbils are produced at each leaf axil, and a single plant is capable of producing 200 bulbils in a growing season. Potato-like in appearance, the bulbils may be brown with a warty texture or light tan to gray with a smooth skin. They are generally globose, but occasionally irregularly shaped, and can measure up to 6 inches long. Bulbils may be produced at any time of year, but are most prevalent at the end of the growing season (autumn to winter). After they have dropped from the vine, the bulbils typically undergo a period of dormancy, sprouting at the beginning of the next growing season.
Native to tropical Africa, Asia, the Pacific Islands and northern Australia, air potato is now naturalized throughout the West Indies and tropical America. In the United States, it is found in Hawaii, Texas, Louisiana, Mississippi, Alabama, Georgia and Florida. Sensitivity to freezing temperatures has limited its expansion into more temperate areas.
Air potato occurs throughout Florida from Monroe County in the south to Escambia County in the western panhandle. It is most often found on disturbed sites, but also invades natural habitats including hammocks and pinelands.
In Florida, air potato is most likely to be confused with Dioscorea alata, another noxious weed species, which is commonly known as the winged, white or greater yam. Winged yam can be distinguished by its clockwise twining habit, quadrangular (often winged) stems, opposite leaves and aerial tubers that are fewer in number and more elongate in shape. Our native species of yam (D. floridana and D. villosa) are lower climbing vines with smaller leaves (to 6 inches long) and never form aerial tubers.
In areas where both staminate and carpellate plants are present, dispersal is by both winged, airborne seeds and by bulbils. In Florida, bulbils spread by gravity and float on water currents. They are also dispersed by heavy machinery and through movement of contaminated brush and soil.
Air potato is said to have been introduced to the Americas from Africa during the slave trade. In 1905, a USDA sample was sent to Florida as an ornamental for assessment, and its rampant growth and potential invasiveness under Florida growing conditions was quickly noted. Vines form impenetrable thickets that overgrow, break and sometimes topple trees and shade out smaller native understory plants, eventually altering community ecology. This species was added to Florida's noxious weed list in 1999.
In its native range, both the underground and aerial tubers are used in traditional folk medicine and may be consumed after processing to remove bitter, potentially toxic constituents. There are also domesticated varieties that produce edible tubers. However, the variety that is naturalized here in Florida contains several potential toxins (including alkaloids, saponins and tannins), and should be regarded as poisonous.