The ruby cactus is originally from South America. This is a grafted cactus, which means it is actually two plants merged together. The green bottom is the only part that produces chlorophyll and is thus what keeps the plant alive through photosynthesis. The lack of green chlorophyll is also part of why the top is red. Caring for this type of cactus is more nuanced than simply watering it occasionally. The red top prefers indirect sunlight while the bottom prefers to be directly in the sun, making it tricky to position this cactus on the window shelf. The ruby cactus should be thoroughly drained when being watered and the soil should dry out completely between watering. During the winter, the cactus should be misted occasionally instead of watered.