Gac is a woody, perennial plant with vining stems reaching 6 m or more in length. Growing from tuberous roots, the vines are often seen climbing on fences or into the tops of trees. Its large (10-15 cm wide), dark green leaves have three to five lobes. Gac is dioecious, meaning that some plants will have female flowers and others will have male flowers. Fruits are ovate (egg-shaped), 10-15 cm long X 10 cm wide, and covered in small spines. Green, immature fruits turn bright orange or red when ripe. Just under the spiny skin is a 1 to 2 cm thick layer of yellow to orange flesh called the mesocarp. Beneath this layer, the inner portion of the fruit is filled with numerous (usually 15 to 20) nearly flat (≈ 2 cm wide), brown to black seeds. Each seed is covered by an oily, red membrane/sac (aril), the edible and most nutritious part of the fruit.
Fruit is about 13 cm in length and 10 cm in diameter.