The Saguaro Cactus is a cactus that spawns in Desert Biomes. It is a lighter green than vanilla cacti and it grows differently. There are a few ways the Saguaro will grow. Both consist of it growing 'arms'.
After it rains, Saguaro's will grow Saguaro fruits, which can be planted on sand to grow another Saguaro Cactus. The fruit can also be eaten.
Sometimes a Saguaro may become invisible. You can see the outline of each individual block of the cactus if you look directly at it within mining distance.