Björnbär, Rubus fruticosus, is ’blackberry’. Björn is ‘bear’ and both words come from Germanic *beran ‘the brown one’, from Indoeuropean *bhero-, ‘brown’. Probably people did not dare to use the old Indoeuropean name *rksos, Latin ursus, for the same reason as the wolf has been called varg and then gråben in Sweden – too dangerous to use the real name.
Bär is ‘berry’ and both words come from a Germanic root *basjom, of unknown origin.
Latin rubus ‘blackberry’ is probably related to rubus, ‘red’. I thought fruticosus was related to ‘fruit’, but no, it means ‘bushy’, from frutex ‘bush’.
According to Den virtuella floran fruticosus has been used as a collective name for lots of blackberry subspecies, in Sweden at least thirty different ones. The wild ones we have here don’t usually give much berries, they are small and most of the time they become dry before they ripen. But this year is very different. In spite of the drought they are many and wonderfully juicy.