Hechtia caerulea is the top 2 photos
One of my favorite Hechtia's is caerulea and tillandsioides. Why? No spines to eat you. Hechtia caerulea has small lavender flowers and Hechtia tillandsioides small white flowers. They look the same until they come in to flower, Hechtia tillandsioides is a larger plant of the two. I could be wrong about the names of these two plants. I have seen the name Hechtia lindmanioides and purpusii also for these plants and also the differences may just be male and female plants. I an really confused about that they are. But I like them.