Scientific name: Gomphocarpus physocarpus E. Meyer seus.lat.

Synonym: Asclepias physocarpa (E.Meyer) Schlechter; A. fruticosa auct. Non L.; Gomphocarpus brasiliensis auct. Non Fourn.

Common name: Cotton Bush, Balloon cotton bush

Family: Asclepiadaceae

Origin:

Native of southern Africa.

Habit:

Perennial shrub with erect branches growing to 2 m.

Habitat:

Weed of disturbed sites (common on roadsides and in rundown pastures).

General description:

Stems and leaves

Stems erect to 2 m, covered with short soft hairs. Poisonous white milky sap exudes from damaged stems or leaves. Leaves are narrow (narrowly ovate to narrowly elliptic) with a pointed tip and wedge-shaped base 3-12 × 0.5-1.5 cm. undersides often lighter coloured and finely hairy.

Flowers and fruit

Individual flowers have five white petals 0.8-1.1 cm long and a star-like structure at the centre. The flowers are borne in clusters (umbels). Fruits are balloon-like 5-7.5 cm long with soft 7-10 mm spines on their surface. Seeds are wind dispersed and have a tuft of silky hairs to carry them. the seeds are black.

Distinguishing features:

Shrub with erect branches, narrow leaves and clusters of white flowers with star-like centres. Distinctive soft spiny balloon-like fruits containing many black seeds with fluffy tufts. Stems and leaves exude milky latex when damaged. Care should be taken since the sap is poisonous.

Noxious status:

Declared noxious as Asclepias physocarpa in Western Australia.

Sources:

Kleinschmidt, H.E., Holland, A. and Simpson, P. (1996). Suburban Weeds. 3rd Edition. Department of Primary Industries, Brisbane.

Parsons, W.T. and Cuthbertson, E.G. (1992). Noxious Weeds of Australia. Inkata Press, Melbourne.

Stanley, T.E. and Ross, E.M. (1983-1989). Flora of South-eastern Queensland. Volume 2. Department of Primary Industries, Brisbane.

Auld, B.A. and Medd, R.W. (1996). Weeds: An Illustrated Botanical Guide to Weeds of Australia. Inkata Press, Sydney.