While attending organic farming workshops, and as a vendor in a Farmer's Market; one of the things which I have learned has been a little about 'Aronia prunifolia'.
They are native to Eastern North America. The Aronia family has many wild varieties which produce berries from red to blue to purple to black.
They are very high in antioxidant pigment compounds, like anthocyanins; and they are high in vitamin C.
Their common name comes from the astringency and bitter flavour of the fruits "chokeberry". None of the varieties produce any sweet berries.
The berries can be used to make wine, jam, syrup, juice, soft spreads, tea and tinctures. Traditional pemmican is made with them.
In the wild they often grow mixed in with blueberries. Commercial producers usually hire crews of pickers to pick wild blueberries, they routinely pick them together. So it is very common to find in a box of commercial blueberries, if you went through them one by one, that as many as a quarter of them may actually be chokeberries.
We live in a blueberry producing region. We see two types of blueberry producers. Some have huge hilly slopes covered with wild growing ground-cover berries, they are sprayed with pesticides or herbicides on occasion, but otherwise the only time anyone goes out there is the crews of immigrant pickers, they pick whatever berries they find.
Small producers will sometimes spend more time weeding their fields and removing the chokeberry plants; so you can find some blueberries out there that will be pure blueberries. These are tended fields of planted berries, working them is more intensive to weed out competing plants; and therefore they will produce boxes of blueberries that are pure.
If you can buy your blueberries from a roadside stand or farmers market, you stand a much better chance of buying only sweet blueberries.
If you buy from a grocery store berries that were shipped from a corporation, you are probably better off to avoid eating them one by one. Use them instead in recipes where you mix the juices, blending them together, so the chokeberries are not noticeable.