Weed Alert - Water Mimosa

Water Mimosa (Neptunia oleracea and Neptunia plena)**

These two aquatic weeds have recently been found in South-east Queensland and are collectively known as Water Mimosa. Water Mimosa are Class 1 declared pest plants in Queensland. Class 1 pests established in Queensland are subject to eradication from the state. Landowners must keep their land free of this Class 1 pest. It is a serious offence to import, introduce, keep or supply a Class 1 pest without a permit issued by Biosecurity Queensland. Penalties of up to $80,000 apply.

Water Mimosa originates in the tropics of Central and South America, and is also grown widely in tropical Asia where it is used as a vegetable. It grows in still or sluggish water, or on damp ground. Water Mimosa can grow rapidly, forming dense mats of vegetation that can:

• restrict water flow and impede movement;
• increase water loss by evapotranspiration;
• reduce water quality by decreasing light penetration and oxygenation;
• cause the death and displacement of native water plants and fish and
• create favourable habitat for mosquitoes.

The decrease in water quality created by Neptunia can encourage the growth of other aquatic pest plants, and increase water treatment costs.

Water Mimosa is a floating aquatic perennial that roots in the banks or bottoms of water bodies. Its stems grow out of the water surface and are supported by a spongy fibrous material that covers the stems. A form that grows on damp ground has smaller leaves and flowers, and lacks the spongy tissue that surrounds stems. The olive green leaves are divided, like those on a jacaranda, and are arranged in opposite pairs on the stems. When touched, the leaves ‘close up’ in much the same way as in sensitive plant (Mimosa pudica). Yellow ball-shaped flowers are produced in early summer. Water Mimosa is a perennial plant, but in southeast Queensland, foliage dies back in the winter and the plants regrow from the roots in spring. In more tropical areas, the plants do not die back.

Look for Water Mimosa in farm dams, canals, drainage lines and slow-moving creeks.

If you think you have seen this plant, ring Biosecurity Queensland immediately on 13 25 23. More information on Water Mimosa is available on the Biosecurity Queensland web site at www.dpi.qld.gov.au

Images © The State of Queensland, Department of Employment, Economic Development and Innovation (2010).