Rivinia appears to be a fairly common misspelling of Rivina. It's spelled (incorrectly) as Rivinia on The Plant List, which would explain how it got into the database here.
You're welcome, Kent. I wanted to make sure I posted my pictures in the right place. Fortunately, I took these pics at MOSI and they did a blog article featuring this plant and used Rivina humilis so I was pretty sure that was correct.
