On Friday 20 February I posted about this weed, thinking it was already in Darebin Parklands, where we walk most days, but I was spotting the wrong water plant. The government website says;
Alligator weed Alternanthera philoxeroides is an Argentinean plant that was first reported in Australia in the 1940s and has since spread along the east coast. If not controlled, the weed can completely cover the surface of water bodies and wetlands, affecting native flora and fauna and agriculture.Matt said it has the potential to be disastrous in Victoria but it's not prevalent in our park yet. His advice to anyone who thinks they've found the plant is to report it to the rangers, but not to touch it, because it reproduces from any little bit. Here's a picture of it.
(I found this photo at the New Zealand site of Environment Waikato and I believe the picture was copyright free for non-commercial use.)
The main distinguishing features of the weed are the fact that two leaves come out at the same spot on the stem and that there are white flowers near the top. The flowers are really a little cluster of flowers and to me they felt quite spiky when Matt passed a plant around the meeting.
I guess Penny and I should keep our eyes open when we walk next time. I wouldn't want this plant to smother our lovely creek.