I believe the leaf that goes with it is the one at the bottom of the picture (not the 3 leaved thing out to the side). Perhaps something in the genus Collinsonia? Here is a link that might be useful: Collinsonia serotina

You have some bloodroot around these plants - the ones with the interestingly lobed leaves. They are a choice native wild flower. FataMorgana

It looks like some sort of impatiens. I found a French page with some likely candidates, Impatiens balfourii and I. glandulifera, which are identified as aliens to the south Massif Central: http://causses-cevennes.com/flore/Cevennes.htm Below is another link, to a page on our native North American impatienses, the jewelweeds. Here is a link that might be useful: Jewelweed -- pictures, uses, commentary

Yep, not a native wildflower, it is native to Eurasia. But it has naturalized pretty much everywhere in the temperate world :-) As tom mentioned it is seldom considered a 'true' invasive as it does not really crowd out native plant growth but it does self seed with abandon and many consider it more of a weed than a valuable garden plant. But it IS sold for that purpose :-) Lunaria annua (money plant, honesty) and Centranthus ruber (Jupiter's beard or red valeran) are very similar in this regard - often planted intentionally but just as frequently seen popping up along roadsides or in untended spaces.