Cactus petal

I have photographed flowers of this cactus (Acanthocalycium violaceum) before, but this time I thought I'd like to show the tip of the petal.

At first glance, it looks damaged, but the tip of the petal is relatively tough and scale-like with a point at the end. This is the only part of the petal that is exposed before the bud opens. For protection against herbivores, the bud has spines on the ends of the covering bracts, just like the rest of the plant. The tips of the petals are similarly protected.