Alligator Weed

Alternanthera philoxeroides

Family: Amaranthaceae

Type of weed: ,

Flower colour(s):

Priority Weed Regional Priority Weed. (See more weeds of the class.)

Flowering Months: , , , ,


A perennial herb growing either as a terrestrial or free floating aquatic plant.

Stems are hollow, leaves are dark green, fleshy, waxy and linear to 70 mm long and 40 mm wide narrowing at the tip.

Silvery white flower heads appear on stalks approximately 7 cm long, rising from leaf axils, papery when mature, mid summer to autumn.

Seeds from the fruit are not viable in Australia.

Don’t confuse with…

Alligator weed can be confused with the native Alternanthera denticulata.


Dense mats produce roots at nodes, which are easily broken off from the main plan and take root downstream, establishing new colonies.

On land, dispersal is usually by stem fragments, or in contaminated turf or in dumped garden waste.

Impact on bushland

On creek lines and in water bodies the plant forms a dense, interwoven mat that covers the surface, blocks water flow, changes water chemistry and adversely affects aquatic plants and animals.

On land the plant becomes dominant in moist areas, replacing native species.


. Lower Mountains including creek lines on the escarpment. Also in South Woodford and South Katoomba.

Alternative planting

Native plants

Alternative plants for moist areas on land include:

  • Bidgy Widgy (Acaena novae-zelandiae)
  • Native Violet (Violaceae hederacea)
  • Water Fern (Blechnum nudum)

Council provides a tool, on its Mountain Landscapes website, to help you choose native alternative plantings. Choose your village, soil, vegetation community and the purpose of your planting, and the tool will give you suggestions.

There are native nurseries in several Blue Mountains villages, including Glenbrook, Lawson and Katoomba. Please also ask at your favourite local nursery.


  • Notify Council

Specific control tips for this weed

If the weed is part of a new infestation, notify the Urban Weeds Team on 4780 5000 as soon as possible.

Do not move the plant; it will grow from the tiniest piece.

For key points on these techniques:

Regional Priority Weed

Control measures:

  • The plant should be eradicated from the land, which must be kept free of the plant.
  • The plant should be fully and continuously suppressed and destroyed.