Alternanthera philoxeroides (Mart.) Griseb.

Alligator Weed

Goett. Abh. 24: 36 (1879) APNI

Taxonomic status:Accepted

Occurrence status:Present

Establishment means:Naturalised

Scrambling, stoloniferous, aquatic or terrestrial perennial to 50 cm high, glabrous, stems hollow, to 10 m long, rooting at nodes. Leaves obovate to narrowly elliptic, 20–70 mm long, 10–20 mm wide; margins entire. Flowers in axillary or terminal subglobose spikes, 8–10 mm long, pedunculate; peduncle to 5 cm long; bracts and bractoles ovate, acute to accuminate, c. 3 mm long; tepals equal, elliptic, 4–6 mm long, white; anthers 5, staminodes 5. Fruit not seen. Flowers Sept.–Mar.

*CVU, *GipP, *Gold, *HSF, *NIS, *OtP, *VRiv, *VVP, *WaP. Also naturalised Qld, NSW, ACT. Native of South America. Weed of urban waterways around Melbourne and regional centres (e.g. Bendigo, Warragul).

Alligator Weed is a state prohibited weed in Victoria and a declared noxious weed in Australia. Infestations smother vegetation and can cause blockages in waterways. Any sightings of this species should be reported for eradication.   

Created by: Andre Messina, 2015-05-07
Updated by: Val Stajsic, 2018-04-18
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Distribution map


Source: AVH (2014). Australia's Virtual Herbarium, Council of Heads of Australasian Herbaria, <>. Find Alternanthera philoxeroides in AVH ; Victorian Biodiversity Atlas, © The State of Victoria, Department of Environment and Primary Industries (published Dec. 2014) Find Alternanthera philoxeroides in Victorian Biodiversity Atlas
  Bioregion Occurrence status Establishment means
Victorian Volcanic Plain present naturalised
Victorian Riverina present naturalised
Gippsland Plain present naturalised
Otway Plain present naturalised
Warrnambool Plain present naturalised
Goldfields present naturalised
Central Victorian Uplands present naturalised
Northern Inland Slopes present naturalised
Highlands-Southern Fall present naturalised

State distribution

Distribution map
Western Australia
New South Wales
Australian Capital Territory