FFF plant ID quiz has readers stumped!

Well, it has been a long time since the plant hotshots who read this blog didn't score the right answer on a plant ID quiz in about 10 nanoseconds, but apparently this one has you stumped.  It's not even remotely related to nightshades or cucurbits, the two maybe guesses so far.  Here's a taxonomic clue - it's closest relatives may be the dogwoods, but it's often classified in its own family.