No one knows for sure why some cacti form this crested shape. As I mentioned in a previous post aboutanother crested cactus I own, there are various theories, but it appears to be an accident of nature.
This Austrocylindropuntia subulata F. cristate is very fast growing. It started as a small single cactus in a four-inch pot just two years ago, has since grown to fill this eight-inch pot, and has produced several new crested pads. It keeps the little needle-like leaves year round.
It thrives on neglect. I don’t water it often, and have never fertilized it because fertilization will sometimes cause cristate cacti to split. When this specimen produced offshoots, they appeared to be a normally shaped A. subulata, but after a while, the crests began to appear.
I have a normal Austrocylindropuntia subulata that I wrote about recently, so check out the photo to see what that looks like. You would never guess they are of the same genus and species!