We've been looking to see the flowers on this Helwingia japonica for almost a year. The sign says it's monoecious, which means we should see some female flowers, and I'd imagined I was seeing some, but the Photo of the Day writeup says the garden's two Helwingia are male. That writeup also says that the flowers are borne on the leaf itself. Some writeup said the leaf petiole and flower pedicel are fused to the point where the flower emerges. I don't know if that's saying the same thing or not. Here's a new link for an abstract of the Dickinson article. I'm guessing the triangular bits are petals and not sepals? Where there are 3 petals, there are 3 stamens between the petals; where 4 petals, 4 stamens.
I've missed the Helwingia peak bloom this year. Here are two photos, May 25. This photo is from 2013, same day as the first ones posted in this thread. I questioned then whether these flowers have petals. I can't find now something I read that said, working from the outside in, there are always sepals, but there might not be petals. Is that true? So then these flowers have no petals? Nothing I've read says that, including Flora of China.