The proximal petal looks white to me. If you enlarge the photo you will see that some of the flower parts overlap the petal and are out of focus and the blurr gives it a blueish tint. I saw nothing, other than the photo in the link you gave that indicates a pointed petal. It could be a variation or an illusion cause by curling. I seen plenty of photos online that show a rounded petal. That said, I did some more search and although I find nothing in literature that say C. erecta has striped spathes, I have seen photos showing stripes (assuming that they were accurately identified) so that's a possibility. Also look at the photo again I notice that the leaves are very long and narrow compared to most C. communis photos I see online. So there is definitely room for doubt in that photo also, it very well be C. erecta. But that brings us back to the same problem of not enough info. There is enough to raise doubt to the ID, but not enough to make a positive ID. As far as hierarchy is concerned I don't know of any. Understanding that plants can be variable, you have to take the info as a whole not just bit and pieces that these photos present.
