In the nature many odd things happen during the fall. When about half of the chlorophyll has broken down anthocyanin production and accumulation begins. We know that anthocyanins are responsible for the red colors in the plants – however, in the science world there are numerous theories of the ecological function of this reaction, and that is still an unraveled puzzle. Read more about the fascinating Nature’s Palette in David Lee’s book about The Science of Plant Color.
All we know for sure that anthocyanines are not poisonous:
Rosehips are commonly used for culinary purposes especially in Northern Europe.