Can not identify this berry.
Found these growing under and around elderberries, I am not sure about the size of the bush/tree, but these were picked about 5 feet off the ground. Everything I've looked at keeps bringing me back to chokeberries, but while chokeberries appear to have a defined butt (bloom end?) these are complete smooth, with some showing only a slight discoloration, but still smooth "scar". They also have only a slightly purple stem, seemingly much shorter and less colorful than the pictures I've found of chokeberries. The berries grow in small non-symmetrical bunches from individual stems that all originate from a larger small branch. The leaves are green on the upperside and purple on the underside. The berry skin is thin, but fairly tough, with a sweet green pulp and they each have, in comparison to the amount of pulp, and size of the berry, a large single seed. They seem to be perfectly ripe now 8/22/16, while the elderberries are only 1/3 to 1/2 ripe. Thank you for any help you can give me and thank you for your time.
Jefferson County Colorado
I'm sorry to be responding to you question so late. Your plant is a Chokecherry, Prunus virginiana. It has a single large seed. https://plants.usda.gov/plantguide/pdf/cs_prvi.pdf . There are varieties, such as "Canada Red" that have reddish/purple leaves.
The fruit of the Chokeberry, Aronia melanocarpa, is a pome. Each pome contains 1-5 small seeds. https://plants.usda.gov/plantguide/pdf/pg_arme6.pdf