Quick Facts

Quick facts

• Arrowhead (Sagittaria montevidensis) is an aquatic annual or perennial herb to about 1 m tall and is distinguished by strongly arrow-shaped adult leaves, and white 3-petalled flowers.
• It is found in shallowly flooded or marshy areas along rivers and streams and occurs commonly in drainage ditches, rice fields and swamps associated with irrigation systems.
• In Australia, it is a serious weed of the rice fields in the Murrumbidgee Irrigation Area.
• It is spread by seed from the movement of water and mud.
• It is controlled by the use of herbicides.

What Does It Look Like?

What is it?

Arrowhead (Sagittaria montevidensis) is an erect tufted aquatic annual or short-lived perennial to about 1 m tall, with 2–12 whorls of flowers at the apex. There are two kinds of leaves, emergent and submerged. The emergent leaves, which rise out of the water, are broadly arrow-shaped to 25 cm long and 20 cm wide, with long basal lobes. The submerged leaves are strap-like and translucent.

The flowers are white, sometimes with a purple patch in the centre, about 2.5 cm wide and in whorls of three, that is, three flowers arising from the same position on the stem. The lower whorls are female and the upper ones male. Both male and female flowers have 3 petals.

The fruit is a cluster about 2 cm wide with 1-seeded segments, each seed being flattened, winged and 2–3 mm long. The roots are brown and fibrous when growing as annuals but with short fleshy rhizomes (underground stems) when growing as perennials (Parsons & Cuthbertson 2001; Thorp & Wilson 1998–; Department of Agriculture and Food undated). Two subspecies of Arrowhead (Sagittaria montevidensis) have been identified in Australia. They are Sagittaria subsp. montevidensis in which the petals are white with a purple patch at the base, and Sagittaria subsp. calycina, in which the petals are white only. There are other differences in internal flower structure (see Parsons & Cuthbertson 2001).

For further information and assistance with identification of Arrowhead contact the herbarium in your state or territory.

Flower colour

White

Growth form (weed type/habit)

Herb, Aquatic

Where it currently grows? Preferred habitat

Arrowhead is found in shallowly flooded or marshy areas along rivers and streams. It is often cultivated in garden ponds and occurs commonly in drainage ditches, rice fields and swamps associated with irrigation systems (Parsons & Cuthbertson 2001; Thorp & Wilson 1998–).

Are there similar species?

Arrowhead may be confused with Sagittaria platyphylla, Vallisneria species, Ottelia ovalifolia and Alisma plantago-aquatica, as the submerged strap leaves of Arrowhead are similar to the juvenile leaves of these three species (Thorp & Wilson 1998–). The arrow-head shape of the emergent leaves of Arrowhead is distinctive.

Why Is It A Weed?

What are its impacts?

Agriculture: Dense infestations of Arrowhead block channels and drainage ditches, and are becoming an increasing problem in rice fields. It is not yet an abundant weed in Australia, although its spread via the rice fields of the Murrumbidgee Irrigation Area is likely (Parsons & Cuthbertson 2001; Thorp & Wilson 1998 – ).

How does it spread?

In Australia, Arrowhead spreads by seed. The seeds move in water along channels and ditches, and in mud sticking to animals, machinery, clothes and footwear (Parsons & Cuthbertson 2001; Thorp & Wilson 1998–).

What is its history in Australia?

It is not known when Arrowhead was introduced into Australia, but it was first observed as a garden escape near Sydney in 1962 (Parsons & Cuthbertson 2001).

How To Manage It?

Best practice management

Chemical control: Herbicides enable good control of Arrowhead (Parsons & Cuthbertson 2001). Please see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au 

Physical control: See more at NSW Weedwise https://weeds.dpi.nsw.gov.au/Weeds/Arrowhead 

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

The seeds of Arrowhead germinate in spring and plants mature during summer, producing flowers from January to March. Seeds mature in autumn and plants die in early winter (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

NSW

What areas within states and territories is it found?

Except for its presence in the Murrumbidgee Irrigation Area in New South Wales, Arrowhead (Sagittaria montevidensis) is not naturalised anywhere else in Australia (Parsons & Cuthbertson 2001).

Where does it originate?

Arrowhead is a native of North and South America and is used widely as an ornamental in many countries. It is a common weed of Californian rice fields (Parsons & Cuthbertson 2001).

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

NO

Where is it a declared weed?

NSW, SA, TAS, WA

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Sagittaria montevidensis

Other scientific names (synonyms)?

Does it have other known common name(s)?

Californian Arrowhead, Sagittaria