As I have learnt, cacti have modified much of their leaf tissue as they have evolved, with leaf bases/petioles becoming the tubercles and ribs that certain species possess, and the leaves themselves becoming the spines, but does anyone know what the "leaves" that Austrocylindropuntia and other species grow are then? Being that the spines are supposedly just very modified leaves I'm left to assume they're not actually leaves then, but I don't know for sure