It seems to me that most of the arguments about beauty go in one of two directions-- mathematically measurable symmetry factors (including everything from the average length of a flower petal in a given blossom to fractals & the golden ratio) or "it's all subjective".

Personally, I have never seen a flower I didn't find beautiful that I recall. I just did an image search for "ugly flowers" and I didn't see a single one I didn't like. Perhaps the subjectivity argument carries more weight in the end.