I'm starting to feel like I've gone through the looking glass... The most I can say on this one is that it's growing on the side of a steep hill above the irrigation canal; I've never seen anything like it. I can't find it in my South American Flora books, either. The flowers are only 3-4 cm across, but the stamens are a good 10 cm long. Any help would be appreciated; I'll monitor the shrub to see if fruit develops.
Wow, that really looks like it! I would never have suspected capers. Thanks, TonyR! Tacca was close, but the petal arrangement was all wrong.