June 2011 Giant Arrowhead Sagittaria montevidensis
WHAT IS IT? A perennial aquatic herb with emergent
arrow-head shaped leaves Often cultivated in garden ponds, and was cultivated for its edible rhizomes by native Americans. Other sagittaria species are cultivated for their edible rhizomes in Asia Not yet an abundant weed in Australia, but is becoming an increasing problem in New South Wales Also known as: California arrowhead, sagittaria, arrowhead, montevideo- pfeilkraut, seta-montevidensis Sagittaria montevidensis Photo by Oeropium S. montevidensis (c) 2005 André Karwath (http://commons.wikimedia.org/wiki/User:Aka) (http://commons.wikimedia.org/wiki/User:Aka )
:Aka)
WHY IS IT A PROBLEM? Capable of infesting irrigation and drainage ditches as well as natural aquatic and semi-aquatic environments As a short-lived plant, dense infestations produce decomposing vegetation, which cause de-oxygenation of water, and increase populations of disease-carrying insects Lowers light levels, shading out aquatic flora and fauna
S. montevidensis infestation. Photo by Dennis Stevenson http://www.plantsystematics.org/imgs/dws/r/Alismataceae_Sagittaria_montevidensis_25627.html- S. montevidensis. Photo by Andre Karwath aka Aka 27/8/2005
What are State Alert Weeds? These are invasive weeds that are not known to be in South Australia, or if present, occur in low numbers in a restricted area, and are still capable of being eradicated. An Alert Weed would pose a serious threat to the State’s primary industries, natural environments or human health if it became established here. All Alert Weeds are declared under the Natural Resources Management Act 2004: their transport and sale are prohibited (Sect. 175 and 177), plants must be destroyed (Sect. 182), and if found on your land their presence must be notified to NRM authorities (Sect. 180) – refer overleaf.
DESCRIPTION Flower close-up. Photo by Richard A. Howard Image Collection, courtesy of Smithsonian Institution. A short-lived perennial aquatic herb growing to one metre high, however in Australia it can live as an annual with a fibrous root system. Submerged, floating and emergent leaves on spongy, buoyant stems (a mechanism that aids flotation), emerge from the base of the plant. White 3-petalled flowers grow on leafless stems mainly in summer.
HOW IT SPREADS
Spread by seed (maturing in autumn), which is transported via waterways, or in mud adhering to clothing and footwear, animals, and machinery.
Giant arrowhead seed. Julia Scher, USDA PHIS PPQ, Bugwood.org HABITAT Found in warm temperate swamps and marshy areas along river and stream banks, drainage ditches shallowly flooded areas, and rice fields.
ORIGIN Arrowhead is native to North and South America.
DISTRIBUTION IN AUSTRALIA Current: Naturalised in NSW, where it is a serious problem in the rice fields in the Murrumbidgee Irrigation Area.
Potential: Irrigation areas and streams in the southern States. In South Australia it might be found along the Murray or in the streams and drains of the South-east.
HOW IT GOT HERE DISTRIBUTION Giant arrowhead was first observed as a garden escape near Sydney in Current distribution based on 1962, but the date of its introduction to Australia, presumably as an herbarium records aquatic ornamental, is unknown.
Potential distribution based on climate modelling WHAT CAN YOU DO? Be on the alert for this plant using this Fact Sheet as a guide. If you see a suspicious plant that may be this State Alert Weed, please report it to your local Natural Resources Management (NRM) Board (contact details at www.nrm.sa.gov.au). For more information on weeds, including Alerts, contact your local NRM Board or visit either www.pir.sa.gov.au/biosecurity (phone 08 8303 9620) or www.weeds.org.au.
Disclaimer: This publication is provided for the purpose of disseminating information relating to scientific and technical matters. The Government of South Australia does not accept liability for any loss and/or damage, including financial loss, resulting from the reliance upon any information, advice or recommendations contained in this publication. The contents of this publication should not necessarily be taken to represent the views of the participating organisations.