This beautiful little flower is known locally as Azedinha (little sour). English names include Purple Creeping Wood Sorrel and Creeping Purple Lady's Sorrel. It seems to be of European origin and its scientific name is Oxalis corniculatavariantatropurpurea. It's quite small, each petal is around 2cm long. You can eat it and it also has medicinal use. Dedicated to PG. ♥
Santa Catarina, Brazil. Articles about the flower: 
This purple flower looks really beautiful. You are right with the flower being European. Here in Germany, we have the more common version of it with the yellow little flowers. It could be found in forests and gardens. Could be for one year or longer. Ignorant people usually consider it as a weed and try to exterminate it as it is multiplied with the seed blown by the wind. Yes, you are right. It is a wild medical plant. It is good for digestion as a tea, good be used as kitchen spice/salad herb, can be employed for skin diseases like allergic reactions (e.g. Neurodermitis etc.) and itching insect-stings.