In 60 years of gardening, I’ve yet to seen a nursery that offers Acanthus spinosus, who actually has the correct plant. 100% of everything in the commercial trade is actually a hybrid of Acanthus hungaricus and A. spinosus, which looks nothing like the true species.
Even authoritative on-line reference sites which should know better, all show the wrong plant, identified as Acanthus spinosus. To make matters more confusing, there is also a hybrid of Acanthus mollis x spinosus in the trade, known by the name Acanthus x spinosissimus. The more prevalent hybrid I mentioned earlier has yet to get a published notospecific name. Perhaps the name Acanthus x spinaricus would make sense.
Below is our plant of the true Acanthus spinosus this month, grown from seed wild collected in Greece, where it grows natively. Perhaps one day, we’ll have enough to share. Since no one has grown the correct plant, the reported hardiness data you find on-line and in reference books is worthless. We’d guess Zone 7a-9b, at least.