Purple Mukunawenna, Alternanthera pulchella, Alternanthera versicolor

This plant looks like alligator weed (Alternanthera sessilis), but it is a relative of it. Alligator weed has hollow stems this one has solid stems. Alligatorweed is poisonous according to a landcare,  (ginninderralandcare.org.au) however, the tropical edible plant database lists it as perfectly edible, you decide: http://tropical plants