Like dirty snow too early in the year. The banks of the Dordogne are covered in a mass of tiny white flowers. Common Michaelmas Daisy (Symphyotrichum x salignum) is an American and it looks like it is happy to be in France.
It colonizes the banks of rivers. It takes only a few years to cover a whole surface with dense and chaotic vegetation, by means of its rhizomes that go everywhere. An invasive species is supposed to make life difficult for indigenous species, thus Common Michaelmas Daisy is considered to be an invasive. Since 200 years it lives in France, but only recently it spreads really fast. Why? Maybe because the long and warm autumns of the last few years helped it grow and flower during a long time? Should you call it a pest? That would be exaggerated, or?
Large stalks stand up or lay down, here they are draped over a dead branch. They carry loose clusters of composite flowers.
Ligulate flowers are whitish with often a tinge of pale lilac, and the tubular flowers, nearly invisible in the image, are yellow. The stem is more or less hairy.
In the background you see the trunks of some Ash-leaved Maples (Acer negundo), a very common tree in the river woodlands of the Dordogne. This one is also an invasive species of northamerican origins.