Dragon fruit is most commonly used as the triangular green base on grafted cacti with colorful red or pink balls. Dragon fruit, aka, Pitaya, or Strawberry pear is a climbing cactus native to the tropical and subtropical forests of Central and South America. Due to the pervasive semiepiphytic habit, dragon fruit is commercially cultivated on topped palm trucks. I purchased seeds for three varieties (yellow, white, and red) from TradeWindsFruit a while ago. So far. only the red type have germinated. When a first planted the seeds I noticed some seedlings, that curiously resembled tomatoes (?!) it wasn’t until they were about a week old that I sheepishly realized, “if it looks like tomato, smells like tomato, and was planted in recycled soil, it is tomato.” Here are my six month old red dragon fruit seedlings. I’m assume it is normal, but both of the plants have been putting out both three and four-sided growth.
It is unclear which genus the yellow pitaya, Selenicereus Megalanthus, belongs to. Dave’s Garden PlantFiles uses the genus Selenicereus, while Wikipedia cites the name as, Hylocereus Megalanthus, both use the species name Megalanthus, meaning large flowered. Selenicereus translates waxy moon, possibly referring to nine inch (23cm) diameter flowers that open at night. All dragon fruit bloom at night, similar to Cereus the night blooming cactus, which is why dragon fruit is sometimes referred to as Cereus Undatus. Personally, I think Waxy moon makes more sense than Hylocerceus, which means waxy wood.
I have never attempted to grow dragon fruit from the grafted cactus, but I have read it readily grows from the rootstock if the red ball is removed.