Though the plant is South African in origin it has become naturalised in the warm temperate zones of Australia. It is a weed of grasslands and disturbed sites in partial shade or full sun and may be spotted growing along road verges and railway lines. This photograph was taken alongside a busy road where the patch of plants was roughly 4 metres by 1 metre, hardly plague proportions.
It is a short-lived perennial shrub growing half a metre to 2 metres high. The leaves are mid green, 10 cm long and narrow, and arranged in opposite pairs along the stem. Like other members of the Asclepiadaceae the plant exudes a milky sap if the stem is broken or cut, which contains cardiac glycosides.
When working amongst these plants protective clothing is suggested, as some people have an allergic reaction to the sap. In South Africa the plant has a history of use in traditional African medicine. The dried leaves and roots were used to alleviate headaches and the Afrikaans settlers used the dried seeds as tinder.
The 15mm, tiny, creamy-white flowers with purple coronas fall in clusters from the leaf axils near the end of the stems. The bush continues producing flowers throughout spring and early summer and, though small, the sheer numbers of the flowers make them very attractive indeed.
These develop into large inflated bladder- like balls, which become straw coloured with age and then later split to disperse the seeds on the wind.
Compared to the size of the flowers the seed pod is enormous, being 60 mm long or thereabouts.
These oval, slightly pointed fruits are sparsely coated with soft protuberances.
I hesitate to name them spikes or prickles because that has unpleasant connotations, whereas these are rather soft and rubbery against the skin, even when dried.
The fruits are the cause of the common names swan plant and cotton bush. Using your imagination one could make a swan out of the bend of the stem and the green seed pod but the cotton bush epithet is more easily understood, because when the fruit splits to disperse the wind borne seeds they look very much like an open cotton boll. They have no relationship to cotton however.
Many find the fruits attractive in their own right and they are often used in floral arrangements or floated in bowls in place of flowers.
Gomphocarpus fruticosus makes it onto the Noxious Weeds List for Western Australia and onto the Australia wide Weeds List. This is because the plant is poisonous if eaten by domesticated animals and is an expensive nuisance if it contaminates a crop.
The leaves are not poisonous to all living creatures however. The Danaus plexippus butterfly spends the larval stage of its life munching on those very leaves which cause problems to domesticated animals.
The larvae are beautiful and fascinating in their own right. Instead of a flower arrangement a branch of Gomphocarpus fruticosus, complete with caterpillars and pupa, make a very unusual living arrangement.
Just be sure to pack the edges of your vase with something like screwed up newspaper, poked in firmly, otherwise the caterpillars may drown if they decide to go walk about. It is very exciting for adults and children alike to watch the life cycle of caterpillar to adult butterfly. Be sure to warn children that all parts of the plant are poisonous to them.
Those of us who are lucky enough to have space to set aside for a wild garden can enjoy the sheer beauty of the caterpillars, butterflies, flowers; and even those bizarre seedpods, outside.
So though Gomphocarpus fruticosus is listed as a noxious weed let’s allow it to grow along railway embankments or road verges. There it spreads in a contained manner, and is just about eaten bare by the end of summer. The adult butterflies then bring pleasure and enjoyment to many people.
Whilst neither Gomphocarpus fruticosus nor Danaus plexippus are natives to Australia if that is going to be held against them then most of us are going to have to pack up and move out with them.