Air yam (Dioscorea bulbifera)

Common Names: air yam, aerial yam, potato yam, bitter yam, cheeky yam

Description:

Air yam (Dioscorea bulbifera) is a fast-growing vine in the yam family, native to Africa and Asia, that climbs high into trees and smothers the plants beneath it [2, 6]. It is best known for the small, potato-like aerial tubers ? called bulbils ? that hang from its stems and sprout into new vines wherever they fall [2, 4]. Brought to Florida in the early 1900s, air yam is now one of the most damaging invasive vines in the southeastern United States [2, 6].

Habit:

Air yam is a twining vine with large, heart-shaped leaves and slender green stems that can climb 60 feet or more into the tree canopy [2, 3]. The most reliable feature is the cluster of small, potato-like bulbils that form along the stems where the leaves attach ? they look like little potatoes hanging in the air, which gives the plant its name [2, 4].

The vine emerges from underground tubers in spring and grows explosively through summer. Bulbils form in mid- to late summer, enlarge through early fall, and then drop to the ground [4, 5]. The above-ground vine dies back with the first frost, leaving the bulbils and underground tubers to sprout the following spring [5, 7]. Late summer and early fall ? when the bulbils are visible on the vine but before they drop ? is the easiest time to find the plant and the best time to remove it [4].

At-a-glance cues:

1. Small, round, potato-like bulbils hanging from the stems where leaves attach [2, 4]
2. Heart-shaped leaves arranged singly (alternate) along the stem, with veins that all spread from the base [2, 3]
3. Slender green stems that twine and climb high into shrubs and trees [2]
4. No spines or thorns on the stems [3]

Leaves:

1. Arrangement: alternate ? single leaves spaced along the stem, not paired [2, 3]
2. Shape: broadly heart-shaped, with a long pointed tip and rounded lobes at the base [2, 3]
3. Size: about 2 to 8 inches (5 to 20 cm) long, sometimes larger [3]
4. Veins: 7 to 11 prominent veins that all arise from the leaf base and arch toward the tip ? a key feature [2, 3]
5. Margin: smooth (untoothed); surface hairless [3]
6. Leaf stalk: long, with a base that clasps the stem [3]

Stems:

1. Habit: herbaceous twining vine that climbs by wrapping around supports, reaching 60 to 65 feet (about 20 m) into the canopy [2, 3]
2. Twining direction: twists to the left (counterclockwise) as it climbs ? the opposite of some look-alike yams [2]
3. Cross-section: round, or only slightly angled; without wings [2, 3]
4. Surface: green, hairless, and without spines or thorns [3]

Flowers:

1. Air yam has separate male and female plants; in the United States most plants are female, so the vine flowers only rarely [2, 3]
2. Color and size: small, greenish-white, and fragrant [3]
3. Arrangement: in slender, drooping clusters that hang from the leaf axils [2, 3]
4. Bloom time: late summer into early fall, when flowering occurs at all [3]

Fruit and seeds:

1. Air yam rarely produces fruit or seed in the United States, because most plants here are female [2, 3]
2. The main reproductive structure is the aerial tuber, or bulbil ? a small, roundish, potato-like growth that forms along the stems in the leaf axils [2, 4]
3. Bulbils range from less than half an inch to several inches across, with a smooth to slightly warty surface, tan to dark brown [3, 4]
4. A single vine can produce hundreds of bulbils in one season, and even small ones sprout readily ? without needing soil, light, or water [5]
5. The plant also grows from a fleshy underground tuber that resprouts each year [2, 3]

Habitat:

Air yam grows in sunny to partly shaded, disturbed places: forest edges and canopy gaps, hardwood forests, fence rows, roadsides, stream and pond margins, vacant lots, and the edges of yards and parks [2, 7]. It prefers moist soils rich in organic matter and does not tolerate salt, so it is largely absent from coastal sites [3, 7].

The species is native to the warmer parts of Africa and Asia [1, 2]. It was brought to Florida in the early 1900s and is now established across the southeastern United States, including Florida, Georgia, Alabama, Mississippi, Louisiana, Texas, Hawaii, and Puerto Rico [2, 6]. Air yam is frost-sensitive: its vines are killed by hard freezes, and it cannot survive the cold winters of the Great Lakes region [3, 5]. In the Midwest, the cold-hardy look-alike Chinese yam (Dioscorea polystachya) is the yam vine more likely to be found [3].

Reproduction:

Air yam spreads almost entirely without seeds. New plants grow from its bulbils ? the potato-like aerial tubers ? and from pieces of its underground tuber [2, 4]. The bulbils are the main way it reaches new ground: they drop from the vine and roll downhill, float and travel in water, get carried on mowers and equipment, and ride along in dumped yard waste and moved soil [4, 7]. People have also spread it on purpose by planting it as an unusual ornamental ? which is why it should never be planted [2].

The vine grows with remarkable speed, up to about 8 inches a day, quickly reaching the top of the canopy [4]. Bulbils form in mid- to late summer and drop in fall, and a single vine can drop hundreds of them in one season [4, 5]. Because even small bulbils sprout and the underground tuber resprouts from fragments, removing every bulbil and tuber is essential ? and control usually takes several years of repeated effort [4].

Impact and Damage:

Despite looking like small potatoes, air yam's bulbils and tubers are not safe to eat. In their wild form they are bitter and contain compounds that can damage the liver, and raw bulbils have caused poisoning in people [9]. They should not be eaten by people or pets, and they are easy to mistake for the edible tubers of cultivated yams ? so it is important not to forage them [2, 9].

In yards and natural areas alike, air yam is a smothering vine. It grows over shrubs, fences, and small trees and climbs high into the canopy, forming dense curtains of leaves that block sunlight from the plants below [2, 7]. This shading kills tree seedlings and can overwhelm mature trees, and it crowds out native wildflowers, shrubs, and groundcover [2, 7]. In Florida it is ranked among the most damaging invasive plants and has taken over large areas of forest and urban natural land [2]. Once established, its underground tubers and abundant bulbils make it very hard to remove [4].

Similar species:

Several heart-leaved vines can be mistaken for air yam, and the bulbils plus the leaf arrangement are the quickest way to tell them apart.

The native wild yam (Dioscorea villosa) has similar heart-shaped leaves but never produces aerial bulbils, and its leaf stalks do not clasp the stem [3, 10].

Chinese yam, or cinnamon vine (Dioscorea polystachya), is a separate invasive vine and the one most likely to be found in the Midwest and Great Lakes region. Its leaves often become paired (opposite) higher up the vine, where air yam's stay single; its bulbils are much smaller; and its flowers smell of cinnamon [3]. It is far more cold-hardy than air yam [3].

Winged yam (Dioscorea alata) has stems that are square and broadly winged and twines in the opposite direction [2, 3].

Greenbrier vines (Smilax species) have only three to five main leaf veins rather than the many veins of air yam, are often woody, and usually carry thorns; they never bear aerial bulbils [3].

Monitoring and rapid response:

Signs to watch for:

1. Late summer and early fall: clusters of small, potato-like bulbils hanging from the stems where leaves attach ? the clearest sign, and the cue that it is time to act before they drop [2, 4]
2. Spring and summer: heart-shaped leaves on fast-growing vines twining up shrubs, fences, and trees [2]
3. Year-round: dense curtains of dead or living vine draped over vegetation, and fallen bulbils on the ground beneath [4, 7]

What you can do:

1. Collect and bag the bulbils by hand in late summer and fall, before and as they drop ? this is the single most important step, since each bulbil can start a new vine [4]
2. Pull or cut the vines, and dig out the underground tubers; tubers are easiest to find in spring when they sprout [2, 4]
3. Bag all bulbils and tubers and put them in the trash, or freeze them for at least 48 hours first ? never add them to a compost pile, where they will sprout [4]
4. Repeat the removal every year, because bulbils and tubers left behind will regrow; several years of effort are usually needed [4]
5. Natural area crews managing larger infestations combine repeated mechanical removal across a site with the air yam leaf beetle (Lilioceris cheni), a host-specific beetle from Asia that was approved by USDA and released in the southeastern United States, where it feeds only on air yam and sharply reduces vine growth and bulbil production [8]

When to call a professional:

1. If the vine has climbed high into mature trees or covers a large area [2]
2. If yearly hand-removal is not keeping the infestation in check [4]
3. To ask about the availability of the air yam leaf beetle for biological control in your area [8]
4. For chemical control options, contact a licensed applicator or your local cooperative extension office.

Report sightings to MISIN. Help track this species' spread by submitting observations through the MISIN web site or the MISIN mobile app (Android, iOS, Windows, and macOS). Photos at multiple angles paired with a precise GPS location are the most valuable data for confirming new occurrences and triggering rapid-response review.

Credits:

1. Plants of the World Online (POWO), Royal Botanic Gardens, Kew. "Dioscorea bulbifera L." powo.science.kew.org
2. Langeland KA, et al. University of Florida IFAS. "Air-potato, Dioscorea bulbifera" (AG112 / Natural Area Weeds). ask.ifas.ufl.edu
3. University of Florida IFAS Assessment / Plant Directory. "Dioscorea bulbifera (air potato)." plant-directory.ifas.ufl.edu
4. Florida Department of Agriculture and Consumer Services (FDACS). "Air Potato Vine Management Guide." fdacs.gov
5. USDA Agricultural Research Service, Invasive Plant Research Laboratory. "Dioscorea bulbifera (Air Potato)." ars.usda.gov
6. USDA National Invasive Species Information Center. "Air Potato." invasivespeciesinfo.gov
7. IUCN Invasive Species Specialist Group. "Dioscorea bulbifera." Global Invasive Species Database. iucngisd.org
8. University of Florida IFAS. "Air Potato Leaf Beetle, Lilioceris cheni" (EENY-547). edis.ifas.ufl.edu
9. Murugan M, et al. "Bioactivity, toxicity and detoxification of Dioscorea bulbifera: a review." Phytochemistry Reviews. scholars.hkbu.edu.hk
10. Texas Invasive Species Institute / Texas Invasives. "Dioscorea bulbifera ? air yam." texasinvasives.org

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