Balloon Plant, Balloon milkweed, Balloon Wild Cotton Gomphocarpus physocarpus, Asclepias physocarpa
(Balmelkbossie, Balbossie, Wilde Kapok)
Order: Gentianales. Family: Apocynaceae. Subfamily: Asclepiadoideae
iMfolozi Game Reserve, KwaZulu-Natal
Balloonplant with capsules, Hluhluwe Game Reserve, KwaZulu-Natal
Hluhluwe Game Reserve, KwaZulu-NatalDescription
This milkweed is a tender perennial, an upright, soft shrub 0.5 to 2 m tall with a fibrous rootstock and with a tree like form. Branches arise above a small, single-stemmed trunk. The branches are pale yellowish green and hollow. The leaves are light green, opposite, and narrowly oblong to lance-shaped.
Cream to white flowers in pendulous clusters are borne almost throughout the year but mainly during summer (November to April). The flowers are attractive and have a complicated structure. The petals bend strongly backwards, arching over the flower. In the centre of the flower is the corona, consisting of five pouched lobes that develop from the petals. The petals are white and the corona is suffused with pink or purple. The corona surrounds the male (stamens) and female (carpels composed of ovary, style & stigma) structures. The filaments of the stamens are fused to form a staminal column which encloses the female part. The female part consists of two free carpels, the tips of which are united and enlarged to form the style head. This is the yellowish, 5-lobed disc that can be seen at the centre of the flower. The anthers are fused to the style head. The pollen grains of each anther lobe are united to form two waxy masses known as pollinia or pollen sacs.
Flowers are followed by large spherical inflated fruits covered with soft spines, splitting to release many seeds, each with a tuft of long silky hairs attached at one end.
When broken, all parts of this plant exude milky white latex that is poisonous if ingested.Taxonomy
The terminology for this plant is a little confusing. It is a native milkweed of South Africa and in 2001 its name was changed from Asclepias physocarpa
to Gomphocarpus physocarpus
to reflect that it is in the family of African milkweeds.Gomphocarpus
was previously in the family Asclepiadaceae, but this family is now classified as a subfamily, Asclepiadoideae, in the family Apocynaceae. Members of the Asclepiadoideae have highly specialised flowers with complicated pollination mechanisms, and include the milkweeds (Asclepias, Gomphocarpus, Xysmalobium), carrion flowers (Stapelia, Huernia and Hoodia) and curiosities like Bushman's pipe (Ceropegia spp.).Distribution
Widespread in South Africa, occurring in the Western Cape, Eastern Cape, Kwa-Zulu Natal, Mpumalanga, Gauteng, Limpopo, North West, as well as in Swaziland, Botswana, Zimbabwe and Mozambique and northwards to Kenya. Habitat
It is found growing in grassland and bushveld, often along roadsides and in disturbed areas, from the coast to 900 m above sea level. Although naturalised and widespread in South Africa for some time, it is an introduced weed, native to tropical Africa.Ecology
Pollination of Gomphocarpus physocarpus
and its Asclepiad relatives is highly specialised. It usually involves trapping the leg or proboscis of the pollinator so that the pollinia get attached to it, and then a similar process, in the next flower visited, to trap the insect again but this time to remove the pollinia. This species is pollinated by a wide variety of vespid wasps in the genera Belonogaster and Polistes. G. physocarpus
is self-incompatible (i.e. it cannot set seed unless it receives pollen from a different plant), yet is also a successful weed in many places far from its original home.
The seeds are dispersed by wind, aided by the tuft of silky hairs attached to each seed.Gomphocarpus physocarpus
is a food plant for the larva of the African Monarch Butterfly
(Danaus chrysippus orientis
). The caterpillars are immune to the poisonous alkaloids in Gomphocarpus and have developed the ability to store them and pass them on to the pupa and adult butterfly, which use them to their own advantage and are foul-tasting and poisonous to predators. The anti-predator strategy of Gomphocarpus has thus been hijacked by the African monarch.