I had photos in our database of the plant from Belgium which is very abundant over here, I even had one sprouting in one of my plant pots last year!
Really strange I didn't recognize the plant, the flowers/ seedheads of the Belgian ones are much smaller and more abundant, look more 'weedy', the plants in Rio looked more like a perennial, more sturdy..How growing conditions can influence the looks of a plant!
Horseweed (Erigeron canadensis)
