This plant grows on my balcony in Vienna, Austria. It gained most of it’s current height (30-35cm) during the last 2 weeks. Before I didn’t notice it. It is covered with tiny white hairs. I conducted a couple of tests. They never stung. The leaves are toothed (I believe “serrate” is the official terminus for this type of edge).
Edit: Now, in July, that is about 2 months later, it bears flowers. Furthermore it is about 3 times taller. I believe there were seed heads, which have been blown and washed away. All of this would fit Conyza mentioned in the comments, but the shape and density leaves appear to differ from C. boranensis or C. canadensis.