Pincushion cactus (mammillaria) This is a very small cactus that has pepper shaped fruit during season. While they resemble a pepper they are actually quite tart. Once ripe they are easily picked off the cactus. They can also be used in a tea. I have heard the stems of this cacti are edible once roasted (spines removed of course). I haven't actually done this myself though. I've only ever consumed the small fruits.