LUDWIGIA PERUVIANA (ONAGRACEAE) IN THE BOTANY WETLANDS NEAR SYDNEY, AUSTRALIA

Ludwigia peruviana is an aquatic shrubby species introduced from the A mericas and spreading to wetlands in coastal south-eastern Australia. It has become dominant, replacing much of the former vegetation in the Botany Wetlands, a series of shallow urban swamps and lakes near Sydn ey, Australia. Studies of L. peruviana were essential to the developme nt of a management plan for the Botany Wetlands. Ecological studies we re conducted in situ and supplemented by a series of germination and g rowth experiments in controlled environments. Flowering peaked in earl y autumn. Seed production for 1990-91 was similar to 450000 seeds m(-2 ) and there was also similar to 65000 seeds m(-2) in the soil seed ban k and similar to 300000 seeds m(-2) in old fruits that remained on the stems over winter. The seeds are similar to 0.8 mm long, weigh simila r to 0.05 mg, are hydrophobic, usually germinate while afloat, and are easily dispersed by water, machinery and birds. Viability of fresh se ed was 99% (tetrazolium dye test), and similar to 20% of seeds were do rmant. Dormancy appeared to break down within two years. Propagation a nd dispersal may also occur by means of stem pieces that produce new s hoots. New plants from seed, seedlings or stem fragments may become es tablished on strand lines or form floating islands that may eventually become stranded. Management needs to focus on control of the seedling s and soil seed bank.