Cereus peruvianus - night-blooming cereus|
Close-up of the side stem. Likes full sun. I water this during it's growing season, with just the occasional splash in winter.
This needs complete darkness at night to flower.
It makes large white flowers in the summer that open at night, hence the moniker 'night blooming Cereus'. It has a pretty deep blue color when it has plenty of room for its roots; when it gets crowded or stressed the color fades to a blah green and flowers are few and far between.