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Sagittaria

Sagittaria plant

Sagittaria leaf

Sagittaria flower

Sagittaria fruits

Arrowhead

Alisma plant

Alisma leaves

Alisma fl/fruits



BOTANICAL NAME:

Sagittaria platyphylla, previously S. graminea subspecies platyphylla


Family:

Alismataceae

Status:

Sagittaria is declared noxious in class 4 throughout NSW. In the irrigation areas it must be controlled; in other parts of the state it cannot be sold.

Description

Erect perennial herb to 1m high growing in shallow water or on mud at the water's edge. Emergent leaves are lance-shaped, about 25cm long and on stalks of a similar length, arising from the base of the plant. There are also submerged, strap-like leaves. Flowers are white, 3-petalled, 2-3cm across and carried in small heads which arise in the leaf axils, with whorls of branches at right angles to the main stalk. Fruits are about 2cm across, more or less spherical and have a rough surface.

preferred habitat and impacts

Sagittaria grows in shallow water or on mud at the water's edge. It and the related arrowhead are weeds of irrigation channels, where they reduce water flow, and environmental weeds of natural wetlands. They can spread quite rapidly and displace native plants.

An infestation has developed on the Brogo Dam in Bega Valley LCA. It began in the late 1990's and despite eradication efforts and the very low water levels in the dam during the 2002-03 drought, it has persisted in spots around the dam edges. It has also spread into the Brogo River below the dam, where it is now found in backwater pools along the edge of the river. It is quite likely to continue spreading throughout the Brogo-Bega River system.  It is a relatively common weed of stationary and slow-flowing water further north along the coast.

Dispersal


Seed is spread by water, and possibly between water bodies attached to the feet or feathers of waterbirds. It might also be spread in mud on vehicles or boats. Sagittaria species are quite attractive and have been cultivated as ornamental plants for wet areas. This may cause new infestations to arise when unwanted plants are dumped or planted in areas where water flow could carry seed into creeks or wetlands.

look-alikes


Arrowhead (Sagittaria montevidensis) has similar growth habit and flowers but leaves are strongly arrowhead shaped, with a pointed, backward facing lobe on either side of the leaf stalk junction, and the flowers have a dark patch at the base of each petal. Sagittaria sagittifolia is similar to arrowhead, but has creeping stems (stolons) and produces edible underground tubers. Both these plants are introduced, from America and Europe respectively.
A tall native aquatic herb Alisma plantago-aquatica has similar large blade-like leaves, but they are broader than those of sagittaria. Its flower spikes are much taller than the leaves (unlike sagittaria, whose flower stalks are mostly shorter than the leaves), and each flower, although white and 3-petalled, is much smaller (about 1cm across) and less showy than those of sagittaria. It is a widespread but not very common wetland plant in south-east NSW.

control


Most importantly, do not dump unwanted aquatic plants into water bodies, or grow species with weed potential in ornamental ponds or aquaria, or in water bodies such as farm dams from which they might be spread by waterbirds. Do not plant anything into natural water bodies. Some invasive water plants are still sometimes sold by nurseries or pet shops. If you notice this, report the instance to Council, so that the proprietors can be advised that it is illegal to sell these plants.
Once an infestation is established, and has been definitely identified, there are two options, mechanical or chemical control. Plants can be raked to shore and piled on the shore above flood reach under plastic, where they will break down. Vigilance will be needed to ensure that plants do not recover. For large infestations herbicide may be necessary, but a permit will be required from the Environmental Protection Agency to apply any herbicide to a water body. Only a limited number of herbicides are registered for use over water. If you suspect you have an outbreak of an aquatic weed, notify your local weed control authority (usually Council) and take their advice on control methods.