Trichodiadema is a genus of succulent plants of the family Aizoaceae.
Obregonia, the artichoke cactus, is a genus of cacti with a single species, Obregonia denegrii.
 The species is endemic to the state of Tamaulipas in Mexico.

Question: How are Obregonia and  Trichodiadema different from each other?
Answer: genus of cacti