What helps cacti conserve water? Of #1, what methods do not involve protrusions that might restrict air flow? Are closed stoma one of #2?
Cactus
Cactus spines help the plant retain water by reducing air flow around the plant Aerodynamic objects have smooth surfaces  Crassulacean acid metabolism is used by cactuses  Crassulacean acid metabolism is when a plant's stomata stay closed during daylight or times of drought to prevent water loss
Family of mostly succulent plants, adapted to dry environments
Would an aerodynamic cactus benefit from more frequently closed stomata?