Impatiens or Vinca?

Did Jeopardy! mix up impatiens with vinca in the Gardening category on April 11, 2016? Flower lover Shelly Bzz on Twitter thinks so:

Dear #jeopardy , You confused flowering vinca for impatiens yesterday in the gardening category. XOXO Flower Lover pic.twitter.com/dsNMPHfzV7

— ShelleyBzzz (@shelleybzzz) April 13, 2016

We also have a question about it from Patti on the recap for that match. To be honest, they all look pretty much alike. All the help we can offer is to show you the image that accompanied the clue, along with images of vinca and periwinkle.

Maybe you can explain how to tell the difference between the three.