Answer: The difference lies not in the color of the berry, but in the way it is connected to the receptacle. When ripe, raspberries separate from their receptacles (the central knob or core), producing a hollow core. Blackberries and other dewberries don't; the core is part of the ripe fruit. One of the distinguishing features between black raspberries and blackberries is that all blackberry stems have vertical grooves, creating an almost angled appearance where black raspberry stems are round. The cross-section of a stem forms a five-pointed star.
You can grow all your berries together in a single garden bed and they will all form fruit true to their genetic makeup. Hope this clarifies things for you.
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