Hey, I was just pointing to what I found. I don't know jack about Arum. However, even if they are synonymous, they could be referring to different varieties of the same species, as taxonomical corrections do tend to take a while to spread throughout the relevant fields. Also, the species is known to be polymorphic, meaning it has more than one naturally occuring form; two different flowers doesn't mean two different species. Look at a typical S. leucophylla flower and and one of leucophylla var. 'Tarnok' - there's a stark contrast in anatomical detail, not just coloration, and yet they're the same species.
Best luck Brad; I'm glad I could help.
~Joe