It is an annual plant resembling the common watermelon.The roots are large, fleshy and perennial leading to a high survival rate thanks to the long tap root. The vine-like stems spread in all directions for a few meters looking for something to climb over. If present, shrubs and herbs are preferred and climbed by means of axiliary branching tendrils. The leaves are very similar to watermelon leaves: they are palmate, angular with 3-7 divided lobes.
The flowers are yellow and solitary in the axes of leaves and are borne by yellow-greenish peduncles. Each has a subcampanulated five-lobed corolla and a five-parted calyx. They are monoecious therefore the male (stamens) and the female reproductive parts (pistils and ovary) are borne in different flowers on the same plant. The male flowers’ calyx is shorter than the corolla. They have 5 stamens, 4 of which are coupled and 1 is single with monadelphous anther. The female flowers have 3 staminoids and a 3-carpels ovary. The two sexes are distinguishable by observing the globular and hairy inferior ovary of the female flowers. A Citrullus colocynthis female flower. Iranian Citrullus colocynthis. Ripe fruit of Citrullus colocynthis.
The fruit is smooth, spheric with a 5–10 cm diameter and extremely bitter at taste. The calyx englobe the yellow-green fruit which becomes marble (yellow stripes) at maturity. The mesocarp is filled with a soft, dry and spongy white pulp, in which the seeds are embedded. Each of the 3 carpels bears 6 seeds. Each plant produces 15 to 30 fruits.
The seeds are grey and 5 mm long and 3 mm wide. They are edible but similarly bitter, nutty-flavored and rich in fat and protein.