Dioscorea is a family of about 630 species, most of which grow in the tropics. They are herbaceous climbers with annual twining stems up to 4m long, and tuberous roots which are generally deep underground.
The Australian Dioscorea transversa is one of our native edible yams. The tuberous roots were eaten by the aborigines, either cooked, or in the case of young tubers, raw. As the roots are deep underground they must be good to be worth the effort of digging them up, without the aid of metal tools. They grow in warm temperate rainforests and moist schlerophyl open forests; mostly along the eastern seaboard of Australia.
They may first draw themselves to your attention with their large papery seed capsules that hang on the plant for many months, maybe even years. They just become more and more old parchment-papery like as time goes by. Of course the actual seed is long gone, just the housing remains.
They have beautiful simple alternate heart-shaped leaves which vary enormously in size and colour, usually 5 – 12 cm long and 2 – 8 cm wide. They have 5 – 7 deep veins along the leaf which help to identify Dioscorea transversa from the other heart-shaped leaves growing alongside them in the rainforest.
The leaves are a real feature of the plant for most of the year as new leaves emerge a bronzy pink and change to a very attractive apple green as the weeks of summer pass.
Male and female flowers are carried on different plants with the flowering season generally from August to November; both male and female flowers hang down in long racemes that blow about in the wind, which presumably aids in the pollination process
The male flowers begin to appear a month or so earlier than the female flowers. .
Male flowers are tiny, with anywhere between 1 to a dozen racemes per axil. Some racemes are very short and others are up to 40 cm long. The flowers last for at least 6 weeks and look like little green seed pearls spaced evenly along the stalk.
In contrast the female racemes have fewer flowers per axil and so they are much shorter. The colour too is quite different. The flower stems are a purplish pink and the tiny little flowers more yellow than green. Close inspection reveals the triangular shape of the coming seed pod already there in the female flower; it just awaits pollination from the male.
Seed pods are formed very quickly once pollination takes place and they swell almost before your eyes into the greeny pink capsules you see in the photograph. The colour merges extremely well into the bush and unless you are searching for them it is surprisingly easy for the eye to glance over and not see them at all.
As they age they become more obvious with a colour change to resemble a sandy, parchment paper
Next time you are walking through or near rainforest look out for Dioscorea transversa.