Gomphocarpus physocarpus E.Mey.

Meyer, E.H.F. (1836) Commentariorum de plantis Africae Australioris 1 : 202. Type: South Africa, J. F. Drege; holo: B ? destroyed. Fide Forster (1996) Flora Australia 28: 218.

Balloon Cotton Bush; Cotton Bush

Usually flowers and fruits as a single-stemmed shrub 1-2 m tall.

Leaves rather variable, leaf blades about 5-8.5 x 0.9-1.3 cm. Stipules dark, small and inconspicuous, less than 1 mm long. Petiole grooved on the upper surface. Leaves, twigs and petioles produce a milky exudate.

Inflorescences not strictly axillary, arising from the twigs beside the petioles but not in the axil of the petiole. Pedicels about 1.5-2 cm long. Flowers about 10-16 mm diam. Anthers sessile. Ovary clothed in glands or glandular hairs. Each flower with two free carpels but only one appears to be functional.

Seeds about 5 x 2 mm, excavated or flat on one side, testa reticulate, long white silky hairs on the margins. Cotyledons yellow-orange.

Cotyledons about 20 x 8-9 mm. First pair of leaves narrowly ovate, opposite. At the tenth leaf stage: leaves linear or narrowly elliptic, apex acute, base attenuate. All parts of the seedling produce a milky exudate. Stipules small and inconspicuous. Seed germination time 8 to 24 days.

An introduced weed originally from Africa now naturalised in NEQ, CEQ and over a wide area of eastern and southern Australia. Altitudinal range from near sea level to 1100 m. In NEQ grows on farmland and disturbed areas of eucalypt forest and occasionally along roads, etc. in rain forest.

A poisonous plant but rarely eaten by domestic animals. Everist (1974).