Sprawling emergent perennial. Forms floating mats on water surface or grows rooted in soil
at water’s edge or in shallow water, extending
many metres across the water surface. Also
grows on land.
- Glossy, spear-shaped, 2–7 cm long
- Smooth margin
- Single, white, papery, ball-like, 1.2–1.4 cm diameter
- On short stalk in leaf axils (stem and leaf junction)
- Aquatic alligator weed: completely hollow
- Terrestrial alligator weed: reddish-brown
Similar looking species
Water primrose (Ludwigia peploides ssp. montevidensis): yellow flowers, alternate glossy leaves
Smart weed (Persicaria decipiens): alternate hairy leaves, dark blotch in centre, small pink
or white flowers on spike.
Senegal tea (Gymnocoronis spilanthoides): irregularly toothed leaf margins, ribbed stems
that are hollow between the joints, halfsphere-shaped (pom-pom-like) white or pale
purple flower heads in clusters
Hygrophila (Hygrophilacostata): stems fourangled, whorled flowers around stem and leaf
- Alternanthera spp: no flower stalks
Alligator weed is native to South America and was first discovered in Australia during the 1940s
in the Hunter River, NSW. It is believed that plant fragments were accidentally introduced via ship’s
ballast water. Alligator weed is regarded as one of Australia’s worst weeds due to its impact invasiveness, capacity to spread and regenerate from fragments, and ability to tolerate a range of
About 5000 hectares in the Greater Sydney and Hunter regions in NSW is infested with alligator
weed. Smaller infestations are found in Vic, Qld, ACT and regional NSW.
Means of spread
Alligator weed does not produce viable seed, and spreads by fragments. Earthmoving equipment, boating equipment and water movement have been responsible for much of the spread, and some infestations may have been deliberately planted.
WoNS. Vic: S; NSW: C2(84)/C3(44); SA: 1@; WA:
P1/2; Tas: D; Qld: C1; NT: A/C; ACT: C1/4
If found, report this weed to your local weed authority.
Source: Recognising Water Weeds
Plant Identification Guide Aquatic Weeds Early Detection Project
Compiled by Jessica Grantley, Fiona McPherson and Andrew Petroeschevsky,
Information contained in this publication may be
copied or reproduced for study, research, information or education purposes, subject to inclusion of an acknowledgement of the source. In particular, the user of this publication agrees to include this copyright notice in any copy made.
The products described in this document are used as examples only and the inclusion or exclusion of any product does not represent any endorsement
of manufacturers or their products by Industry & Investment NSW. Industry & Investment NSW accepts no responsibility for any information provided in this
material. Any questions that users have about particular products or services regarding the subject of this material should be directed to the relevant commercial