I think the line blurs between the two enough that its a confusing line. If the plot is the romance itself (regardless of the abundance or lack of sex scenes) and it has a HEA/HFN, then its a romance. If the sex scenes are used as plot devices to move the romance forward and not just there to entertain or a natural result of the romance, then I would say it's likely an erotic romance. If its romantic, but absent of a HEA/HFN and the romance is not the main point of the plot, but the plot is driven still by the sexual relationships, then I'd say its likely an erotica.
You can have hot sex scenes in a romance, and not be classified as an erotic romance.
An erotica can be very romantic, but not meet the classification of romance and be neither an erotic romance or a romance.
Etc... its sometimes hard to tell. It also varies between publishers. I'd have publishers call some of my erotica, erotic romances. I didn't fight them, since they were publishing me. *lol* But I still think it was erotica, with heavy romantic tones to them. I don't know.... I'm rambling, but my point was what I started this post with... the line is blurry! *lol*