Ficus means fig. From Wiki:

'Common English names for the plant and its fruit are Indian fig opuntia, Barbary fig, cactus pear, prickly pear, and spineless cactus, among many others.'

I was confused, because in my native language (German) the plant is simply called 'Kaktusfeige' (meaning, well, 'Cactus fig').

Ok, the plant is a species of cactus, the correct designation being Opuntia ficus-Indica or prickly pear, which grows everywhere in Sardinia. The figs actually are sold by street vendors along the roads.

I got the correct designation wrong because it was lost in translation, my bad.