There are five different local species of Cayratia, all known as water vines, or sometimes “native grapes”. They are in the grape family, which is obvious if you look at their recognisably “grapey”seeds. Fruits of smooth water vine have just two very large seeds per fruit. These fruits are edible, but said to be not particularly tasty. They can irritate the lining of the throat if eaten in quantity. I’m kicking myself, though, that I wasted this opportunity to try some. It is always risky to put an unknown fruit in your mouth, but I had already checked it for the typical grape seeds, so knew it would be safe.
Smooth water vine is rarely seen here nowadays, but probably once grew in the long-gone rainforests of the Toowoomba City precinct. It can still be found in the rainforest on the southern slope of Mount Tabletop.
It can grow into a large vine, with a stem diameter eventually reaching 10cm. It would make an attractive pergola plant, needing a sheltered site when young, and probably always growing best if it has a cool, well-mulched root-run.
The stems are high in saponins. It is said to be possible to make a good soapy lather in water, suitable for washing clothes and hair, by cutting them into foot-long lengths and heating them till they’re soft .
Smooth water vine has its name from its shiny green leaves. These distinguish it from the very similar “hairy water vine” Cayratia saponaria, which often shares the habitat with its cousin and has softly velvety leaves.
Cayratias grow well in full shade, and make lovely foliage plants for indoor use.