Question: How are Obregonia and  Trichodiadema different from each other?

Context paragraphs:
Trichodiadema: Trichodiadema is a genus of succulent plants of the family Aizoaceae.

Obregonia: 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.

Supporting paragraphs: Obregonia Trichodiadema
Answer: genus of cacti