This bush seems to be very infrequent in the waysides of Pittsburgh compared to the myriad of other plant invaders that have ravaged the wildlands here. It seems to be similar to Aronia which is listed for this County (& which I've never had the pleasure to recognize). The internet berry photos of Aronia all have distinctive 'cringes' on the ends of the berries (remnate of the sepals?). These berries are round w/ no distinct cringe or mark @ the tips of the berries at all. The skin & flesh of the berries are dark purple/ black, & there's several (3 -4?) black seeds in each berry.
Ditto to Rhamnus cathartica. An invasive weed in your part of the world. A rare and declining native over here.
