I appreciate all the research and comments, gang! I have revised the description to include "(thistle?)".
I received the OP coin from CNG today. Ken Dorney is right, the coin looks most like the Roma photo. It doesn't have the slightly brown tone of the Nomos photo and the rough areas in the CNG photo are almost impossible to see in any light. It is a truly gorgeous example and I'm very pleased to have it in my collection!
how did i miss that, absolutely stunning coin @ancientnut ! post your own pic when you get it please, im curious to see what it will look like!
Again => Wow!! => a-nut, that is an amazing Op-coin!! (I'm totally jealous) => hmmm? ... here is a Gallienus example which shows a sweet pomegranate (maybe your symbol is a pomegranate?) Oh, but it could be a thistle (I like thistles too) ... but I doubt that it's a thistle => I'm fairly sure that it's a pomegranate (final answer)
That's an interesting speculation, Steve! It is always described as a flower, but it does resemble a pomegranate with very long spines on top, as on your Gallienus. Hmmmm... chrsmat71, sorry, I don't have decent photographic facilities. The three OP photos will have to suffice.