beware, prickles

What made this sign extra bizarre to me is that it is in the "Garden of the Senses" - a small, wonderful courtyard in Montreal's Botanical Garden designed for the visually impaired. You are supposed to touch and/or smell all the plants - so why have a prickly plant at all, and why is this the only sign in the whole garden without a braille translation!? Otherwise, though, a really great garden and a wonderful idea.