See G.O. Poinar et al., “Tropidogyne pentaptera, sp. nov., a new mid-Cretaceous fossil angiosperm flower in Burmese amber,” Palaeodiversity, 10:135-40, 2017.

"If we have an accurate picture of the evolution of ... challenge most notions of what makes a flower a flower. To see what the first primitive angiosperm might have looked like, I flew to England ...