The Lesser Periwinkle is native to central and southern France but is also seen in Britain where it is often grown in gardens as ground cover, being particularly useful in quite shady places where many plants will not grow. You sometimes find it in the countryside in Britain but that is the result of someone dumping some garden waste at the side of the road and it getting established.
In Poitou-Charentes it grows wild in shady places like hedgerows and woodlands and it flowers early in the year, from March onwards. The flowers are bright blue with a hint of purple/lilac colour. It is in the same family as the Gentians which of course it looks quite similar to. It is a low creeping plant, known as a subshrub, so it is like a very low growing bush, it spreads quite well and can grow up slightly higher if it can use other taller plants to scramble over.
The scientific name is Vinca minor and its French name is Petite Pervenche, or Pervenche Mineure
There is another Periwinkle which is the Greater Periwinkle and this is very similar except that the leaves are bigger and the flowers are bigger. The best way to tell them apart is that the leaves of the greater Periwinkle have tiny hairs along the margins whereas the Lesser Periwinkle is hairless. In both plants the leaves remain present throughout the winter.
If you have trouble identifying other wildflowers from the Poitou-Charentes region then you can look them up on https://poitoucharentesinphotos.wordpress.com/wildflowers-of-poitou-charentes/