Cactus are defined as plants with glochids. The points on this cactus where the spines originate are the glochids. Here is a longer definition:
Glochids or glochidia (singular "glochidium") are hair-like spines or short prickles, generally barbed, found on the areoles of cacti in the sub-family Opuntioideae. Cactus glochids easily detach from the plant and lodge in the skin, causing irritation upon contact. Wikipedia: GlochidI like cactus because they are self-sufficient and survivors.