Weed Identification

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Arrowhead

Sagittaria montevidensis

Family: Alismataceae.

Form: Water plant

Origin: Native of America.

Flowers/Seedhead: Flowers: Mostly white, about 2 cm wide; female flowers carried in groups of 3 ringing the stem, with male flowers in groups above them; all borne on a leafless buoyant spongy stem. Flowers mostly summer.

Description: Tufted annual or short-lived perennial to about 1 m tall, base fleshy. Juvenile submerged leaves strap-like, translucent; emergent leaves on spongy buoyant stems. Fruit a cluster about 2 cm wide with 1-seeded segments; seeds flattened, winged, 23 mm long.

Distinguishing features: Distinguished by strongly arrow-shaped adult leaves, and white 3-petalled flowers.

Dispersal: Seeds spread by water and in mud.

Confused With: Juvenile leaves are similar to the submerged strap leaves of Vallisneria spp. and juvenile leaves of Ottelia ovalifolia and Alisma plantago-aquatica.


Arrow-shaped leaves & 3-petalled white
flowers, Murrami, NSW, Feb

Notes: Mainly grows in inland irrigation areas of NSW, where it is a potential weed of rice, and minor weed of irrigation supply and drainage channels. In the 1980s it increased noticeably in the Murrumbidgee Irrigation Area of NSW. Also in creeks at Shepparton and Cobram. In California it is a common weed of rice. Unlike Alisma lanceolatum and Damasonium minus, Sagittaria montevidensis has poorly developed seed dormancy and may not survive where crop rotation is practised. Two subspecies, ssp. montevidensis and ssp. calycina are present in Australia.

References:

    Noxious Weeds of Australia. W. Parsons and E. Cuthbertson, 1992, pages 3638. Waterplants in Australia. G. Sainty and S. Jacobs, 1994, pages 226227.

Web References: Search Australian web sites for further information on this weed.


3 growth stages, seedling right, juvenile left

Juveniles with
strap-like leaves

Dense growth in
an irrigation channel
Griffith, NSW, Feb

This weed has been included in the WEEDeck field guide as card W10

More information about WEEDeck is available from Sainty & Associates Pty. Ltd.

 

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