|Botanical Name||Sagittaria platyphylla|
DescriptionSagittaria platyphylla is an emergent perennial aquatic plant up to 800 mm in height. It has fleshy rhizomes (creeping roots) which are buried and usually submerged below the water surface, while leaves are held above the surface by rigid stems. There are three growth forms. Of the two with emergent leaves one is linear and the other ovate, both tapering abruptly to a point and are 100 to 250 mm long and 20 to 80 mm wide depending on the form. The stems holding the emergent leaves are up to 550mm long, triangular in cross section and are winged towards the base. The submerged leaves are strap-shaped, up to 500 mm long and 25 mm broad. The distinctive three-petaled white or sometimes pink flowers are 30 mm in diameter and are found in groups of three-flowered whorls at the end of the flower stem. Flowers are always below leaf height and produce clusters of fruitlets which contain oblong seeds, each 1.5 to 3 mm long. Seeds germinate in spring and flowering occurs from November to March during which period the fruits ripen and shed seed. The fleshy roots (rhizomes) remain dormant during winter, their buds shooting in spring.
Where is it found?Sagittaria platyphylla grows in static or slow-moving freshwater such as drains, streams and pond margins, up to a depth of 450 mm.
Why is it a problem?Sagittaria platyphylla forms extensive infestations in shallow waterways, seriously restricting water flow and increasing sedimentation, thus aggravating flooding. It also poses a significant threat to native wetland flora and fauna.
How does it spread?The plant increases density and spreads locally by its creeping root system. It spreads to other areas through seed carried by water, machinery, wildlife and humans, as well as rhizome fragments being transported by ditch cleaning machinery and spoil.
How do I get rid of it?
Plants can be removed manually or mechanically, ensuring all parts of the plant including the root system are removed. Ensure that clearance machinery does not spread seed or plant fragments.
Contact the Regional Council for information on chemical control.
|Recommended Approach||Report to the Bay of Plenty Regional Council|
The plant can be confused with other species of Sagittaria and with water plantain (Alisma plantago - aquatica). However the latter has "D" shaped stems, with broader, more rounded leaves and a taller flowering stem (0.5 - 2 m high) whilst emergent Sagitteria platyphylla has triangular shaped stems.
Sagittaria platyphylla is a National Accord Pest Plant. A native of North America, it has been introduced to many countries as an ornamental aquatic plant. It was first recorded at a field site in New Zealand (on Auckland's North Shore) in 1988.
This plant is prohibited from propagation, sale and distribution within New Zealand!