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Nymphaea mexicana
(Yellow Water Lily)
This water plant is a garden escapee and, as can be seen in the photograph below, taken at Botany Wetlands, Eastlakes in New South Wales (courtesy of www.weeds.org.au), it has a great ability for taking over water bodies. It chokes waterways and especially enjoys water that is rich in nutrients, so it is of particular concern for coastal lagoons.
Nymphaea mexicana is not known to set seed in Australia, so its escape is probably due to dumped garden waste. It is a problem in many areas including around Perth, Fremantle, northern Tasmania, the entire east coast region from the top of Cape York around to coastal South Australia, and coastal Northern Territory. From these outbreaks, it is predicted to widen its range inland. For example, it now appears on the Echuca Landcare Group's website (on the Murray River in northern Victoria).
Appearance
It has the typical water lily type flowers and leaves. Leaves are broad, elliptic and float on the surface, although they can be almost erect when crowded. The yellow flowers grow to about 12cm wide and are produced from spring through to autumn. It is a perennial plant but can die down in winter in some areas.
It spreads via stolons (modified, horizontal stems that produce roots). At each node roots will sprout and a new plant will grow. The plant will grow in water up to 2 metres deep.
There are hybrids of the plant and other Nymphaea species that are suspected of naturalising.
Control
No biological controls are available at present. Unfortunately the best form of control is glyphosate herbicide for aquatic environments, and it can take years to control.
Prevention
Planting suitable native water plants in ponds and dams is preferable. Dumping of garden waste must be avoided. If you suspect you have seen an outbreak, report it to your local Department of Primary Industries, Conservation and Land Management, Parks & Wildlife offices, or other relevant authority.
Information sources:
www.weeds.org.au
http://florabase.calm.wa.gov.au/browse/profile/2922
www.waterwise.nsw.gov.au/water/wetlands_facts_weeds.shtml
Click here to return to the invasive plants list.
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You may not use the information for any other purpose without the express written permission of SGA.