A Yellow Flower Test

Not H. undatus - check geographical distribution again, as well as the number of anthers in the flower. It's actually H. megalanthus, the yellow pitahaya. I've never seen reds growing here in Ecuador, and had always assumed them to be Central American endemics.

And for 8 - Yes, that's the plant. Although I know it by the slightly botanically outdated name "Stapelia mutabilis".

Here's the hint I was about to post for it, along with the answers.

And congrats all on finishing off the stumper!!

 

(AH! So it was an Orbea... amazing... :)