I have a botanical/historical question.

Crusea, Antiphytum, Cordia are all named XX saucerflowers. Does "saucerflower" refer to the shapes of the flowers? Crusea in particular doesn't look very saucer-like to me at all! Did one plant become strongly identified with the name saucerflower and others get compared to it, like how plantain and lily shows up in a lot of common plant names?

Where would I look up this kind of information?