aerial yam

Dioscorea bulbifera var. bulbifera
Vine
Alternate
Simple
Cream
Green
Discoloured

A long-lived vine that produces short-lived climbing stems each year from an underground tuber. Rounded to egg-shaped tubers (1-10 cm across) are produced along these stems. Its alternately arranged leaves (5-30 cm long) are usually heart-shaped with 5-11 prominent veins. Separate male and female flowers are borne on separate plants, with most plants being male. The small flowers are arranged in elongated drooping clusters in the upper leaf forks. These flowers have six cream or greenish 'petals' (1.5-3 mm long).

Family 
Dioscoreaceae
Deciduous 
Flowering time 
Summer-Autumn
Common names 
Also known as: air potato, bitter yam, ganmangu, wild yam,
Origin 
Native to tropical Africa, Madagascar, Mauritius, Reunion, the Indian Sub-continent, eastern and southern China, south-eastern Asia, northern Australia and Christmas Island.
Known distribution 

This species is becoming naturalised beyond its native range (Northern Australia) into south-eastern Queensland and northern New South Wales.

Habitat 

An emerging weed of riparian vegetation, urban bushland and forest margins.

Habit 

A long-lived (i.e. perennial) vine that produces short-lived (i.e. annual) climbing stems each year from an underground tuber. These tubers are egg-shaped (i.e. ovoid), pear-shaped (i.e. pyriform) or rounded (i.e. sub-globose) and usually grow 4-10 cm long. Its climbing stems may reach up to 8 m or more in height.

Stem and leaves 

The climbing stems are rounded or slightly angled, green or purplish-tinged, and hairless (i.e. glabrous). They twine to the left and often produce rounded (i.e. globose) to egg-shaped (i.e. ovoid) tubers in the leaf forks (i.e. axillary bulbils). These stem tubers are greyish-brown or purplish-brown in colour and 1-10 cm across.

The alternately arranged leaves are simple and borne on stalks (i.e. petioles) 2.5-5.5 cm long that clasp the stem at the base. These leaves (5-30 cm long and 2-30 cm wide) are heart-shaped (i.e. cordate), broadly egg-shaped in outline (i.e. broadly ovate), or somewhat circular in shape (i.e. orbicular) with entire margins and pointed tips (i.e. acute or acuminate apices). Their upper surfaces are dark green and glossy, while their undersides are paler and duller in appearance. The leaves are also hairless (i.e. glabrous) and have 5-11 prominent veins from the base.

Flowers and fruits 

Separate male and female flowers are borne on separate plants (i.e. this species in dioecious). The tiny male (i.e. staminate) flowers are borne in elongated, slender, drooping clusters (i.e. pendulous racemes or panicles) 6-13 cm long, with one on more of these clusters being produced in each of the upper leaf forks (i.e. axils). The individual flowers are borne on very short stalks (i.e. pedicels) 1-2 mm long. They have six cream or greenish coloured 'petals' (i.e. tepals or perianth segments) and six stamens. These 'petals' (1.5-3 mm long) turn purplish and then brownish as they age. The female (i.e. pistillate) flowers are also borne in elongated, slender, drooping clusters (i.e. pendulous racemes or panicles) 6-30 cm long, with one on more of these clusters being produced in each of the upper leaf forks (i.e. axils). They have six greenish-white 'petals' (i.e. tepals or perianth segments), six partially-formed stamens (i.e. staminodes), and an ovary topped with a two-lobed stigma. Flowering occurs during late summer and early autumn.

The oblong capsules (12-30 mm long and 10-15 mm wide) are three-winged and turn from green to brown or straw-coloured as they mature. These capsules contain one to several dark brown seeds (12-18 mm long and about 5 mm wide) that have a papery wing at one end. However, the fruit are rarely seen in south-eastern Queensland as most cultivated plants are male.

Reproduction and dispersal 

This species reproduces mainly by stem tubers (i.e. bulbils) and also produces seeds in winged fruit.

The winged fruit may be dispersed by wind and water, while the tubers and fruit are probably both spread in dumped garden waste.

Impact and control methods 
Cut stump
or
Foliar spray

Aerial yam (Dioscorea bulbifera var. bulbifera) is regarded as an environmental weed in south-eastern Queensland and north-eastern New South Wales. In Queensland this species has become naturalised along waterways and in rainforest in the Moreton and Burnett districts (e.g. along the Enoggera Creek catchment in Brisbane and in the Gold Coast Local Government Area). In New South Wales the "invasion and establishment of exotic vines and scramblers" was recently declared as a "key threatening process", and aerial yam (Dioscorea bulbifera var. bulbifera) it is listed among the exotic vine species contributing to this threat.

In Florida aerial yam (Dioscorea bulbifera var. bulbifera) is a serious environmental weed and engulfs native vegetation, climbing high into mature tree canopies. Like Madeira vine (Anredera cordifolia ), it produces large numbers of stem tubers (i.e. bulbils), which facilitate its spread and make it difficult to eradicate.

Native/Exotic 
Exotic
Notifiable 
No
Council declaration 
SIL
Similar species 

Aerial yam (Dioscorea bulbifera var. bulbifera) very similar to winged yam (Dioscorea alata) and relatively similar to native yam (Dioscorea transversa). These species can be distinguished by the following differences:

■aerial yam (Dioscorea bulbifera var. bulbifera) produces tubers (i.e. bulbils) along its stems and its leaves are nearly as wide as they are long (5-30 cm long and 2-30 cm wide). Its stems are not distinctly winged.

■winged yam (Dioscorea alata) produces tubers (i.e. bulbils) along its stems and its leaves are nearly as wide as they are long (4-20 cm long and 4-13 cm wide). Its stems are distinctly winged.

■native yam (Dioscorea transversa) does not produce tubers (i.e. bulbils) along its stems and its leaves are relatively narrow (5-12 cm long and 2-8 cm wide). Its stems are not distinctly winged.