Sagittaria (Sagittaria platyphylla)

Also known as: arrowhead

Sagittaria is an aquatic weed in New South Wales, capable of aggressive growth and rapid spread.

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How does this weed affect you?

Sagittaria spreads quickly and forms dense infestations in wetlands and natural watercourses where it can:

• reduce or change water flows, increasing the risk of flooding
• outcompete native water plants
• reduce water quality
• restrict movement of fish and other aquatic animals
• reduce food and habitat for fish and other aquatic animals
• make recreation activities such as swimming, boating and fishing difficult
• reduce the visual appeal of waterways.

 In irrigation channels and crops it:

• traps silt which gradually fills the channel bed
• limits water flow
• reduces water storage and efficiency of irrigation channels
• can damage infrastructure
• reduces rice yields
• harbours plant viruses.

What does it look like?

Sagittaria is an emergent aquatic plant that belongs to the Alismataceae family. Other similar-looking species in this family include arrowhead (Sagittaria montevidensis), alisma (Alisma lanceolatum), water plantain (Alisma plantago-aquatica) and star fruit (Damasonium minus). Table 1 summarises the differences between sagittaria, arrowhead and these similar-looking species.

Sagittaria is a perennial herb and can grow up to 150 cm tall.

Leaves and stems

Sagittaria has oval/linear shaped leaf blades with pointed tips, up to 25 cm long and 10 cm wide at the top of each stem (leaf stalk). It also has long narrow strap-like submerged leaves up to 50 cm long. Sagittaria stems are triangular in cross-section.

Flowers

Sagittaria flowers appear in whorls or coils. Male flowers are 3 cm across with three white petals and yellow centres. Female flowers have no petals, resembling flattened green berries. Flowers appear below the height of the leaves during spring and autumn.

Fruit/seeds

Sagittaria seeds occur in clusters, consisting of flattened and winged segments, 0.15-0.3 cm long with 1 seed in each segment.

Morphological forms

Sagittaria has three morphological growth forms: submerged rosette, broad-leaved emergent and narrow-leaved emergent. These forms play an important role in the life cycle allowing the species to adapt to varying environmental conditions.

Submerged rosette form of sagittaria

The submerged rosette form develops following germination and can persist for several years without producing erect emergent stems. The emergent form develops when conditions are suitable. The rosette form does not produce flowers or seeds but can produce rhizomes and corms. This is one of the keys to the plant being able to survive and perpetuate without producing emergent stems.

The rosette form is commonly found in deeper water where conditions are unsuitable for the emergent forms. It can also be found interspersed with the emergent forms in dense stands.

Broad-leaved emergent form of sagittaria

Rosettes grow into emergent plants if water height is approximately less than one metre. This may be due to depth-related factors such as light reduction in deeper water which prevents emergent forms developing.

The broad-leaved emergent form arises from an energy-rich rhizome system. It tends to occur in slow-moving parts of channels and streams, along river banks and at the extremities of infestations. Infestations in drains tend to be established from seed, rather than from existing plants. The warm, shallow and slow flowing water in drains favours the settling and germination of seed and the growth of healthy, broad-leaved plants.

Narrow-leaved emergent form of sagittaria

The third form of sagittaria is an emergent form with narrow leaves and an almost grass-like appearance. Compared to the broad-leaved form, these leaves give plants an ‘unhealthy’ appearance, and are thought to arise from depleted rhizomes.

When broad-leaved plants are damaged by flooding, herbicide application or grazing they will re-emerge as the narrow-leaved form. The narrow leaves supply energy to the rhizome through photosynthesis until the rhizome is healthy enough to produce new broad-leaved plants.

Table 1. Distinguishing features of sagittaria, arrowhead and similar-looking species found in NSW.

	SAGITTARIA S. platyphylla	ARROWHEAD S. calycina var. calycina	ALISMA Alisma lanceolatum	WATER PLANTAIN Alisma plantago-aquatica	STAR FRUIT Damasonium minus
Origin	North America	America	Europe, west Asia, north Africa	Native to Australia	Native to Australia
Height	150 cm	100 cm	100 cm	150 cm	100 cm
Distinguishing features	Larger flowers (3 cm wide), oval-shaped leaves with only one main mid-vein	Large flowers (2.5 cm wide), strongly arrow-shaped adult leaves	Narrow leaves and large inflorescence held above the height of the leaves, small flowers (10 mm wide)	Small flowers (10 mm wide), oval-shaped leaves with many veins	Small flowers (6 mm wide), large inflorescence held above leaves
Leaves	Emergent leaves: oval-shaped with a pointed tip; to 25 cm long and 10 cm wide. Submerged leaves: long, narrow strap-like without expanded blades; to 50 cm long	Emergent leaves: arrow-shaped; prominently veined; to 25 cm long and 20 cm wide; lobes to 15 cm long and 10 cm wide. Submerged leaves: strap-like, linear	Spear-shaped; to 20 cm long and 4 cm wide; up to 7 prominent veins connected by several transverse veins. Submerged leaves: strap-like	Oval-shaped; 10-25 cm long and 7-10 cm wide; usually 7 prominent parallel veins connected by numerous transverse veins	Oval-shaped; 5-10 cm long and 1.5-4 cm wide; 3-5 parallel veins connected by numerous finer transverse veins
Stems (leaf stalk)	Triangular in cross-section; to 80 cm long.	Round in cross-section	To 80 cm long; flattened on one side with small wings at the base	To 80 cm long, flattened on one side with small wings at the base	To 30 cm long
Flowers	Appear in whorls or coils. Male flowers: 3 white petals with yellow centre; 3 cm wide. Female: no petals; look like flattened green berries. Flowers appear below the height of the leaves during spring to autumn	Female flowers carried in groups of 3 ringing the stem, with male flowers in groups above them; all borne on a leafless stem. Petals are white. Flowers are 2.5 cm wide	Inflorescence (flower cluster) to 60 cm long and 40 cm wide. Flowers 10 mm diameter. Sepals to 2 mm long. Petals 4 mm long, white or pink. Flowers in summer	Wiry inflorescence (flower cluster), to 60 cm long and 40 cm wide. Flowers 10 mm diameter. Sepals to 2 mm long. Petals 4 mm long, pale pink or almost white. Flowers on long stems above height of leaves	Inflorescence (flower cluster) to 50 cm long. Flowers 6 mm in diameter. Sepals 1 mm long, green. Petals ovate 6 mm long, white or pink. Flowers early summer
Fruit/Seed	Cluster 0.5-1.0 cm across; 1 seeded segment flattened and winged 1.5-3 mm long. Each plant can produce up to 20,000 seeds	Clustered; laterally flattened, 1.5-3 mm long, beaked at the apex with dorsal wings	Triangular; 2-2.5 mm long. Each fruit contains 1 seed	2-2.5 mm long, falling singly	Star-shapedÈ

Where is it found?

Sagittaria grows in southern NSW, particularly in the Murray Irrigation District. It is common in the Greater Sydney and Hunter and also grows on the North Coast region. Isolated infestations are also present:

• near Bingara in the North West
• at Dubbo in the Central West
• at Bega in the South East

Sagittaria is native to North America. It was introduced as an ornamental plant. The first plant was identified in Australia in 1959 near Brisbane.

What type of environment does it grow in?

Sagittaria grows in warm temperate and subtropical climates. It grows best in sites with fluctuating water levels and silty sediment, including small channels and on the inside bends of rivers.

The broadleaf emergent form grows in warm, shallow and slow-flowing water. The submerged rosette form can grow in deeper water than the emergent forms. The different forms can grow together and submerged rosettes may grow amongst crowded broadleaf plants.

Frosts may kill or damage the above-water parts of the plants but the plants can regrow from the submerged parts.

Sagittaria grows in:

• irrigation channels and drains
• creeks and rivers
• lagoons and dams
• wetlands.

Maps and records

• Recorded presence of Sagittaria during property inspections (Map: Biosecurity Information System - Weeds, 2017-2022)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  
• Estimated distribution of Sagittaria in NSW (Map: NSW Noxious Weed Local Control Authorities, 2010)
  Map shows weed distribution and density estimated by local council weeds officers in 2010.

How does it spread?

By seed

The broadleaf form of the plant can produce hundreds of thousands of seeds. Seed can float for up to 3 weeks before sinking and then remain dormant until conditions are right. Seed usually germinate from late winter to spring when there is an ideal amount of light and the outer seed coat has absorbed enough water. As well as flowing water, seeds are spread by animals including livestock and birds.

By plant parts

Sagittaria can reproduce from stems, root fragments, underground rhizomes and corms. These plant parts can be spread by floods or people dumping aquariam or pond plants. Corms are dormant through winter and produce new growth in spring, though they can remain viable in the soil for many years. Corms allow rapid regeneration of sagittaria following periods of stress. 

References

Aquatic Plant Services (2004), The Biology and Control of Arrowhead, Goulburn-Murray Water.

Chapman, M. & Dore, D. (2006). Arrowhead Strategic Plan Final Draft, Gommalibee, Victoria: Rural Plan Pty Ltd.

Crocker, W. (1907), “Germination of seeds of water plants”, Botanical Gazette, Vol. 44, No. 5, pp. 375-380.

Department of Primary Industries Victoria, (2009), Invasiveness assessment - Giant Arrowhead (Sagittaria montevidensis) in Victoria, August 2010 http://www.land.vic.gov.au

Eastern & Western Riverina Noxious Weeds Advisory Group. (2004). Regional Weed Management Plan: Riverina Sagittaria Management Plan

Flower, G. (2003). The Biology and Control of Arrowhead (Sagittaria graminea). River & Catchment Health: Presenting current research in the Goulburn Broken Catchment.

Goulburn-Murray Water. (2001). Arrowhead Sagittaria graminea factsheet , Aquatic Plant Services.

Gunasekera, L. & Krake, K. (2001). Arrowhead – a serious aquatic weed in northern Victoria. In Victorian Landcare and Catchment Management, 19, 7.

Rataj, K. (1972). “Revision of the genus Sagittaria. Part I. (Old World Species)”, Annotationes Zoologicae et Botanicae, 76, pp. 1-36.

Turner, C.E. (2001). “Reproductive Biology of Sagittaria monetividensis Cham. & Schlecht. spp. Calycina (Engelm.) Bogin (Alismataceae)”, Unpublished doctoral dissertation, University of California, Berkeley.

More information

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Control

Physical removal

Physical removal involves excavation with machinery or manual digging by hand. Physical removal allows water movement to be restored quickly in waterways blocked by infestations. It is also a technique used in areas where herbicide use is inappropriate, such as near sensitive waterways or irrigation channels under continual use.

Appropriate hygiene and containment measures must be applied during manual removal to ensure plant fragments do not float downstream and establish elsewhere. It is also important when excavating to ensure the root and rhizome fragments in the soil are removed to avoid future regeneration.

Excavation can be labour intensive and costly and is generally avoided in irrigation channels where it interferes with the engineering structure of the drain. However in new and isolated infestations where eradication is possible mechanical and manual removal should be considered. By removing all viable plant material and following up with removal of regrowth, eradication is possible. Physical removal can be particularly effective to control isolated or new infestations.

Herbicide options

See Using herbicides for more information.

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PERMIT 89861 Expires 31/01/2023
Glyphosate 360 g/L (Only products registered for aquatic use)
Rate: 10 L product/100 L water
Comments: Spot spray. Only for use in Aquatic areas (Irrigation and drainage channels) within the Murrumbidgee Irrigation Limited areas of responsibility. DO NOT exceed a maximum of 40 L product/ha. See permit for other critical comments.
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: 1 tablet for every 37.5 cubic metres of water to achieve 400 parts per billion.
Comments: For use on dense or established weed populations in enclosed water bodies, deeper than 0.5 m and larger than 37.5 cubic metres, or margins of larger, still water bodies. Throw tablets directly into the water to achieve uniform distribution of the herbicide. At least 50% of the weed biomass must be below the water surface. See label for further instructions and restrictions.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Flumioxazin 15 grams /tablet (Clipper herbicide®)
Rate: Inject solution into water body. 1 tablet per 37.5 cubic metres. Each tablet dissolved in at least 20L of water + 0.5 - 1.0% adjuvant/surfactant
Comments: For use on dense or established weeds in water bodies less than 0.5 m deep or with a volume less than 37.5 cubic metres. Dissolve tablets in water (at least 20L per tablet) mix thoroughly and then inject the solution directly into the water body.
Withholding period: 14 days before using treated water to irrigate food crops. See label for withholding periods for other uses of treated water.
Herbicide group: G, Inhibitors of protoporphyrinogen oxidase (PPOs)
Resistance risk: Moderate

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Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW	Prohibition on certain dealings Must not be imported into the state, sold, bartered, exchanged or offered for sale.
Central Tablelands	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
Central West	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found. This Regional Recommended Measure applies to all species of Sagittaria
Hunter	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of new weeds being introduced to their land. Land managers should mitigate spread from their land. The plant should not be bought, sold, grown, carried or released into the environment. Land managers reduce impacts from the plant on priority assets.
Murray	Regional Recommended Measure* (for Regional Priority - Containment) Land managers should mitigate the risk of new weeds being introduced to their land. Plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
North West	Regional Recommended Measure* (for Regional Priority - Asset Protection) Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. Plant should not be bought, sold, grown, carried or released into the environment.
Riverina	Regional Recommended Measure* (for Regional Priority - Eradication) Land managers should mitigate the risk of the plant being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant.
Western	Regional Recommended Measure* (for Regional Priority - Prevention) Land managers should mitigate the risk of new weeds being introduced to their land. The plant should be eradicated from the land and the land kept free of the plant. The plant should not be bought, sold, grown, carried or released into the environment. Notify local control authority if found.
	*To see the Regional Strategic Weeds Management Plans containing demonstrated outcomes that fulfil the general biosecurity duty for this weed click here

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Reviewed 2021