Weed Identification

Australia > > Alisma

Alisma

Alisma lanceolatum

Family: Alismataceae.

Form: Water plant

Origin: Native of Europe, western Asia and northern Africa.

Flowers/Seedhead: Numerous with sepals about 2 mm long and petals about 4 mm long. Flowers summer.

Description: Erect aquatic perennial herb to 1 m high. Leaves variable, submerged leaves strap-like; emergent leaves with up to 7 prominent parallel veins and on a stalk to 80 cm long that is flat on one side and with small wings at the base. Aggregate fruit triangular in outline, individual 1-seeded fruit 22.5 mm long and falling singly.

Distinguishing features: Distinguished by emergent lanceolate leaf blades to 20 (rarely to 21) cm long and to 4 (rarely to 5) cm wide, tapering to base; large open inflorescence to 50 cm long and 30 cm wide and held higher than leaves; flowers bisexual, about 1 cm wide with 3 acute-tipped white or pink petals and 3 smaller green sepals, stamens 6 and style curved towards base; aggregate fruit with 1820 individual fruit rounded at the end furthest from the point of attachment and these fruit in one plane.

Dispersal: Spread by seed and movement of tubers.

Confused With: Alisma plantago-aquatica which has broader leaves and Sagittariaspecies that have narrower inflorescences with flowers in whorls around the inflorescence axis.


Mature flowering plants,
Griffith, NSW, Sept

Notes: Thrives in shallow, slow-moving or stationary, nutrient rich water. A serious weed of rice in New South Wales.

References:

    Waterplants in Australia. G. Sainty and S. Jacobs, 4th edition, 2003, pages 216217. Flora of Victoria.N.Walsh and T. Entwisle (eds), 1994, Vol. 2, pages 125127. Flora of NSW. G. Harden (ed), Vol. 4, 1993, page 18.

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


Seeds

Juveniles,
Hanwood, NSW

Submerged strap-
leaves of seedling

Roots,
Katunga, Vic, Dec

Flowers & immature fruit,
Katunga, Vic, Dec

This weed has been included in the WEEDeck field guide as card W06

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

 

Australia > > Alisma

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