Passiflora foetida is a member of the Passion Fruit family, Passifloraceae. It could have been a native of South America but has since naturalized in most tropical countries, including Singapore. Unlike its relatives, namely, the Giant Granadilla (Passiflora quadrangularis) and the Common Passion Fruit (Passiflora edulis), Passiflora foetida occurs mainly as a weed and it is getting uncommon nowadays as Singapore continues to urbanise. A number of varieties of this plant are known to exist.
Its common names include the Stinking Passion Vine or Wild Water Lemon. Its species name ‘foetida’ has the meaning of “stinking” in Latin which refers to the strong odour that is emitted by damaged foliage. Note that the stems and leaves of this vine are toxic and suspected to have caused poisoning in livestock. Interestingly, the young shoot tips and leaves are also valuable, wild-gathered vegetables in several South East Asian countries where they are thoroughly cooked by boiling first and then consumed in a soup. Leaves have medicinal properties where they are used to treat neurasthenia, insomnia, early menstruation, edema, itching and coughs.
The plant itself, is a vine, like other Passiflora species. The stems of this plant are thin and wiry and covered with numerous sticky hairs. They are herbaceous when young and gradually turn woody with age. Its leaves are three- to five-lobed and hairy to touch too. The flowers of this plant are quite attractive but small in size, about 5 cm in diameter. Flowers are usually white in colour with a purplish center.
The fruits of this species are quite interesting as they are encased with leafy sepals that are finely dissected. Each fruit is about 2 to 3 cm in diameter and they turn from green to orange when ripe. There are varieties which produce fruits that turn red when ripe. The fruits do not split open when ripe. Note that the young fruit is cyanogenic and hence poisonous. They are only edible when ripe and children in rural villages in Singapore decades ago would be able to recall the fun of popping the yellow/orange ripe fruits into their mouths as they play along in the kampong. Each fruit has numerous black seeds embedded in the whitish, sweet pulp where seeds dispersed by birds.
Passiflora foetida is considered as a protocarnivorous plant. When the vine flowers, the leafy sepals that encase the flower are reported to produce sticky, dew-like secretions at the tip ends and these may help the plant to trap insects. There is insufficient evidence to show whether or not, the plant gains any form of nourishment from trapped prey.
This Passiflora species mainly occurs as a weed, sometimes invasive, in wet areas although it can tolerate drought when established. It is common in plantations, rough pastures, roadsides and wasteland. It is a ‘useful’ weed which is sometimes used as a soil cover in plantations to control lalang (Imperata cylindrica) and soil erosion.
It also plays an important ecological role. The young leaves and shoots of Passiflora foetida are consumed by caterpillars of the Leopard Lacewing (Cethosia cyane) and Tawny Coaster (Acraea terpsicore) found locally in Singapore.