The correct answer to this question is "the blackcurrant". The blackberry, according to Wikipedia, is "an edible fruit produced by many species in the genus Rubus in the family Rosaceae"; it therefore doesn't have a unique binomial name.
Wikipedia goes on to say that "the taxonomy of the blackberries has historically been confused because of hybridization and apomixis [replacement of the normal sexual reproduction by asexual reproduction, without fertilisation], so that species have often been grouped together and called species aggregates."
Most experienced quizzers will be aware that Ribes nigrum is the blackcurrant, as this is how Ribena got its name.
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