Pokeweed or Elderberry? Bush with Dark Berries

A rapidly growing summer bush produced dark red/black berries instead of expected flowers. Owner wants to know if it's milkweed, pokeweed, or elderberry.

Expert Possibilities: Could be Pokeweed (Phytolacca americana) or Elderberry (Sambucus). Both have dark berries. Pokeweed berries are in long clusters; elderberries in flat umbels. Take photos to a local garden center for positive ID. Caution: Pokeweed is toxic; elderberries must be cooked.